I think you'll enjoy the Mages Guild questline in Oblivion. It's got a nice "good guys vs. bad guys" feel to it. It's the Mages Guild (the good guys) versus the Necromancers (the bad guys) if you want the short version. Joining the Mages Guild is dirt simple - just ask any of the guildhall stewards. No more of this "x-skill level in this school and y-skill level in that school" nonsense. Just ask to join. If you have a class with low magic skills (like a pure Thief or Warrior), you might get some snide remarks about your suitability (Falcar in Cheydinhal is probably the funniest), but the stewards will all take an "it's your funeral" approach to it and let you in.
Getting in is one thing, but progressing is going to be another issue entirely. The first thing that you're going to have to do is gain a recommendation from each of the guildhall stewards so that you can have access to the Arcane University. Some recommendation quests are quite easy and some are a bit more of a challenge, but you'll need a recommendation from all seven stewards (Anvil, Bravil, Bruma, Cheydinhal, Chorral, Leyawiin, Skingrad). These can be done in any order and at any time, so I'm just going to take an alphabetical approach to it.
Once all seven recommendations are in the bag, hightail it to the Arcane University and talk to Raminus Polus. He'll promote you to Apprentice (with a nice robe to go along with it) and you'll have access to everything in the university except the Orrery ($2 official mod plug-in for that), the Council Chambers and the Arch-Mage's quarters. Polus will also be your quest-giver for the next few quests, so be nice to him.
Anvil Recommendation (minimal difficulty, travel required, situation-dependent combat)
Speak to Carahil. She can usually be found behind the counter when you enter the guildhall. It seems that a rogue mage has been killing merchants along the road between Anvil and Skingrad. She intends to do something about it and decides that you are the ideal candidate to help her (translation: you're expendable and, therefore, suitable bait). She gives you a few Frost Shield scrolls (which turned out to be completely useless for the quest) and sends you to the Brina Cross Inn to meet with Arielle Jurard, a battlemage assigned to deal with the problem. You may already have the inn on your map if you walked from Skingrad to Anvil and can fast-travel. Otherwise, you've got a little bit of a walk ahead of you. Watch out for a highwayman shortly before you get to the inn.
Speak to Arielle before speaking to anyone else. Once the quest stage has been advanced by talking to her, get a room at the inn. It doesn't really matter whether you tell the innkeeper that you're a merchant or not. After you speak to the innkeeper, you'll be forced into a conversation with Caminalda. It also doesn't matter whether you stick with your cover story with Caminalda or not (she's convinced you're a merchant, regardless). Then go up to your room. Arielle will come in to speak with you (I've even had her beat me to the room a couple of times) and give your instructions: rest (you have to rest in order to let the appropriate NPCs disappear from the inn), leave the inn and follow the road going east. Defend yourself, if necessary, but she and her partner will take care of everything else.
This is easier said than done because Arielle and her partner don't have very high Athleticism skills, so you're probably faster than they are if you run. But you shouldn't have any problems if you remain at a walk. Shortly after getting on the road, Caminalda will confront and attack you. In my experience, the Frost Shield scrolls that Carihil gave you are worthless because the first spell Caminalda casts at me is a fire-based spell followed quickly by a summoning of some sort. Your mileage may vary. If you've let Arielle and her partner keep up, they will wade in and can probably take Caminalda down by themselves. If you managed to get significantly ahead of them, you're pretty much on your own. So take her down using whatever means you want. If it helps any, she is unarmored and unarmed and once her magicka runs out, she's toast. Finish up any conversations with Arielle and then report back to Carahil to get your recommendation. Make sure that you pick up Caminalda's room key and clean out the chest.
As an interesting side note, this particular stretch of road is patrolled by Imperial Guards and I have had Caminalda attack me while there was a guard close by. The guard made mincemeat out of her within a few seconds and I still got credit for the quest. I've also had a four-way battle with Arielle, her partner, Caminalda and a guard. Arielle's partner accidentally hit the guard and as soon as the guard finished with Caminalda, he made mincemeat out of Arielle's partner and then Arielle when she tried to help her partner. I decided that discretion was the better part of valor in this case, stood back and let them whack on each other and then cleaned up the loot afterwards. Whether Arielle and partner survive the encounter has no impact on whether you successfully complete the quest or not. As long as Caminalda is pushing up daisies at the end, you're good to go.
Bravil (easy difficulty, travel required, no combat)
Talk to Kud-Ei (the only Argonian in the guildhall and also the quest-giver for the "Through a Nightmare Darkly" miscellaneous quest; please don't pick the wrong quest by mistake - ask about "Recommendation" and not about "Kud-Ei"). There's a bit of tension due to a situation between Varon Vamori and Ardaline. Varon has stolen Ardaline's Mage's Staff and you need to get it back. You'll find Varon either wandering the guildhall, at a local inn, at home or somewhere between those places. He's also a member of the Thieves Guild, so fellow members will have some additional conversation topics with him (and he'll like you better).
Disposition is the key to completing this quest, so you'll get lots of opportunities to play the Persuastion minigame if you want. Although Kud-Ei says "whatever means necessary," she doesn't mean whack him (he doesn't have the staff anyway). Instead, she offers you a "Beguile" scroll. Get his disposition up to 65 or 70 (using either scrolls, Speechcraft or Bribery) to find out that you're dealing with a childish incident over unrequited love. Ardaline did not return his affections, so he became angry and took her staff. He felt guilty about it, but couldn't figure out how to return it, so he sold it to Soris Arenim, a friend in the Imperial City, and now he can't get it back.
You have to go talk to Kud-Ei again and she'll give you some more "Beguile" scrolls. Then it's off to Talos Plaza. I don't know what Arenim's schedule is, so I just break into his house in the wee hours of the morning, but he is home and the door unlocked for a while during the day. Sure it's trespassing if you break in, but getting in and out quickly will avoid a bounty. Arenim won't even talk to you about the staff until you have his disposition up to 70 and even at that, he wants 200 septims for it. Hmmm. There has to be an easier (and cheaper) way of doing things because you're not going to get reimbursed for any of this.
There is - Erissare Arenim, his wife. Get her disposition up to 65 and she'll tell you that the staff is in a locked chest in the basement and that the key is in Soris' desk upstairs. Right, then. Off you go. Grab the key from his desk upstairs and the staff from the basement, and take the staff back to Kud-Ei. Alternatively, you can just pick the lock on chest in the basement, but it's easier to use the key. After you bring back the staff, Kud-Ei will send along your recommendation and teach you the "Captivate" spell.
Bruma (easy difficulty, no travel, no combat)
In order to complete this quest, a "Detect Life" and "Dispel Other" effect is handy, but not required.
Talk to Jeanne Frasoric in the main room about a recommendation and she'll tell you that J'skar seems to have disappared. She suggests talking to the other guildhall members to see if anyone knows anything. Volanaro suspects that a malfunctioning spell may be to blame, but won't provide any other details until you get his dispostion up.
So go talk to the others. You'll have a "Jeanne Frasoric" and a "J'Skar" topic with all of the gulidhall members. Follow up on it to learn that the guildhall steward is not exactly "well respected". She is generally believed to hold her position because she sucked up to the right people, not because she's a particularly skillful mage. Selena Orania is the most tolerant of Jeanne, while Volanaro is the least. There's something else going on. If Volanaro likes you well enough (disposition of 70 or more), he'll let you in on the fact that it's all a prank designed to yank Jeanne's chain and will offer to help you if you will help him with their next prank. So you have to make a choice: either help Volanaro or not.
If you choose not to help, you're on your own. Here's where the "Detect Life" comes in handy - just cast it and look for an effect on something that you can't see. Eventually you will find J'skar. If you don't have the effect available, you can always walk around the guildhall and see whether you get a dialog icon on something that isn't there. It's a bit harder to do it this way, but it can be done. Talk to J'skar and he'll tell you that you're ruining their prank. The problem is that finding J'skar isn't enough to complete the quest. You have to return him to the visible world, and that's where the "Dispel Other" effect comes in. Cast it on J'skar until he turns visible and you can go back and report your success.
If you don't have a "Dispel Other" effect, you'll either need to get it (it's an Apprentice-level Mysticism spell that you can purchase from Alves Uvenin at the Leyawiin guildhall) or you'll have to agree to help Volanaro.
If you choose to help Volanaro, he'll suggest that one good prank deserves another and says that he'll help you if you'll steal Jeanne's copy of "Manual of Spellcraft" from her desk. He'll even teach you an "Open" effect to help you along (it's the same as the "Open Easy Lock" spell called "Minor Latch Crack"). If that's beyond your Alteration ability, you can always resort to lockpicks. Upstairs you go, grab the book and bring it to Volnaro. He'll meet you at 10 p.m., remove J'skar's invisibility and you can go report success to Jeanne. Either way, your recommendation is in the bag. The only difference is the NPC dialogs.
On a side note, Jeanne likes to stand out in the front room and summon Scamps for a couple of hours every day. If you'd like to work on your Marksman, Destruction or other combat skills, you can wait for her to summon and then attack it. Jeanne's spell duration is only something like 5 or 10 seconds (real time), so the Scamp will disappear before it can do much damage should you fail to kill it in one or two whacks. She also likes to cast Illusion spells on herself. So get yourself a "Dispel Other" and everytime she enchants herself, zap her.
On another side note, the Bruma guildhall is going to get spanked at a later point in the Mages Guild questline. If there are any spells that you'd like to buy from Volanaro or Selena Orania, do it before you get into the Archmage's quests because no one except J'Skar is going to survive the spanking. You might also want to loot the guildhall because a lot of the stuff is going to disappear when the hall is destroyed. Only Selena Orania's alchemical stuff is considered theft.
Cheydinhal (easy difficulty, no travel, no combat)
Talk to Falcar, who wanders around on the ground floor. If you go early enough in the morning, he will be down in the basement, which will make the rest of the quest a bit easier. A Ring of Burden has been dropped down the well behind the guildhall. Deetsan has the key to the well, so be a good fellow and fetch the ring for him. Deetsan certainly has the key but will not give it to you until she talks to you first and she won't do that while Falcar is nearby. So you're either going to have to wait until Falcar is out of earshot (meaning on the other side of the building) or has gone to sleep before she'll talk to you.
It seems that you aren't the only gullible Associate to whom Falcar has assigned this little task. An Associate named Vidkun was also sent after the ring and hasn't been seen since. Deetsan recommends proceeding with caution and teaches you Buoyancy. If you'd like, you can also purchase a couple of Water Breathing potions from the resident alchemst. See, the trick here is that the ring weighs 150 pounds (yeah, I know the Guide says 200 - it's wrong) and you'll probably be over-encumered once you pick it up. So drop all of your armor and weapons just outside the well (no one will bother them) and then go in. The Buoyancy effect is a combination of Feather and Water Breathing and should last long enough for you to get in and back to the guildhall with your prize. Alternatively, and assumning that your Alteration skill is high enough, a normal "Water Breathing" and "Ease Burden" (both Apprentice-level spells) should also do the job.
Once you are in the well, head to the right when you go through the archway and you'll find Vidkun at the end of the short passage (if you go left, you'll be able to pick up a Nirnroot). He's quite dead and has the ring in his inventory. Get it and report back to Deetsan because Falcar is gone. It appears that in her desire to do well by doing good, Deetsan had words with Falcar over the assignment that he gave you and threatened to report him to the Council of Mages. He blew up, threatened Deetsan and the rest of the guildhall and left. Sorry about that, but it seems you won't be getting that recommendation unless Falcar already wrote it.
She gives you a key and sends you to his quarters in the basement to look for your letter or anything "unusual". A thorough search of Falcar's room turns up no letter and nothing unusual unless you open his dresser (which has a red container icon when you look at it). Inside are two Black Soul Gems. Take them (they'll show as stolen in your inventory) and report back to Deetsan. She'll take the gems from you (even if you only brought one, they're both removed from the game) and send them to the Council of Mages along with her recommendation.
Chorral (minimal difficulty, travel required, minimal combat)
Speak to Teekius (the Argonian). He wanders the ground floor all day and sleeps behind a locked door on the third floor at night. Teekius is concered about a mage named Earana who is in town looking for something. He wants you to find out what she wants and get rid of her (as in have her leave town). You'll find Earana in one of two places: on the street outside the guildhall (day) or at the Grey Mare inn (night).
Earana is looking for a book called "Fingers of the Mountain" and believes that it can be found at Cloud Top, a ruin in the mountains north of Chorral. She doesn't want you to discuss this matter with anyone at the Mages Guild, so you'll have to agree to that before she will give you the information that you need and mark Cloud Top on your map. After this conversation, your Journal will tell you to go report this to Teekius (you do want the recommendation, right?) and Teekius will tell you to bring the book to him, not Earana. Since your primary goal here is to get the recommendation, we'll plan on doing that.
Off to Cloud Top you go. Unless you've already been there (doubtful), you'll need to walk rather than fast-travel. Head out the north gate of Chorral and just follow the road. You'll probably run into a couple of overland encounters (wild animals) on the road to Cloud Top, but that should be it because there isn't anything except a charred corpse at Cloud Top itself. Open the corpse and you'll find a book called "Fingers of the Mountain," which you cannot read. Take it back to Teekius. The best time to do this is in the evening when Teekius is asleep. I say this not because it's terribly important, but because it will save you a little time.
Once you give the book to Teekius, the quest is finished as far as he's concerned and your recommendation is on its way to the Council. But the quest isn't finished as far as Earana is concerned. If you delivered the book to Teekius while he was asleep, he'll put the book in the chest next to his bed and go back to sleep (allowing you to swipe it back quickly and easily). If, however, you deliver it to him during the day while he's downstairs, you'll have to wait until he puts it in the chest. Of course, it will be much easier for you to steal the book if you do it while he's downstairs and the third floor is unoccupied, but it's not nearly as much fun as doing it right under his nose (do Argonians even have noses?).
Anyway, once you have the book back (or even if you don't), go talk to Earana. She'll rag on you about giving it to Teekius, but says that you can still have the promised reward if you will bring it to her. Obviously the quest is not scripted to do an inventory check to see whether you have the book, just whether you gave it to Teekius or not). As soon as you finish that part of the conversation and exit, wait a couple of seconds until you get a Journal pop-up telling you to go steal the book back from Teekius. Hopefully you've already done this, will get a Journal update to that effect, and can talk to Earana again to give it to her.
She'll tell you to wait a day for her to do the translation thing and then come see her again. Do that and she'll give you some notes which will start Part II of the quest. Read the notes and follow the instructions. Take a Welkynd Stone to Cloud Top (the stones are available in most Ayleid ruins and there's one just laying loose in an unlocked display case in one of the guildhalls) and cast a Shock-based spell on the pillar. You'll definitely get zapped, so fortifying your health and/or having a Shock-shield effect is recommended. My Breton got nailed for 30 points, so if you assume that I'm getting the benefit of a 50% resistance and plan for getting hit for 60, you'll be good to go. At the end of it all, you'll have a "Finger of the Mountain" spell in your spellbook. This is a targeted, 40-point, area effect, Shock-based Destruction spell that you may or may not be able to cast, depending upon your Destruction skill (minimum 50 required) and available magicka.
You can also take the opposite approach to completing this quest. If you deliver the book to Earana, Teekius will rag on you and send you to steal it back. She's only in her room in the evening, so you can go steal it during the day (let her finish preparing the notes for you) and turn it over to Teekius, which will seal the deal as far as your recommendation goes. The rest of the quest plays out the same as far as getting the spell.
Leyawiin (moderate difficulty, travel required, combat required)
Talk to Dagail, or at least try to. What she says doesn't make a lot of sense and that's the problem. But she does manage to let you know that you should talk to Agata. Agata explains that Dagail's Seer's Stone amulet, which helps her keep the visions and voices under control, has gone missing. Agata suggests that you ask around the guildhall to find out whether anyone has seen it. The other mages point you toward Kalthar. Kalthar definitely has an axe to grind as far as Dagail's appointment as the guildhall steward is concerned and mentions that Dagail's father had a similar problem. Go back and talk to Agata, who is fairly certain that she and Dagail never mentioned the father while Kalthar was around, so Kalthar jumps to the top of the list of prime suspects. Agata suggests that you go talk to Dagail while she keeps an eye on Kalthar.
Dagail doesn't even let you get out the question. She launches in to a semi-incoherent poem that points you toward the fort where her father was stationed. You won't have to do any asking around because your Journal can make sense of her ramblings, even if you can't. You're going to have to get to Fort Blueblood and retrieve her father's amulet. The fort is approximately southeast of Leyawiin and is marked on your map, but you can't fast-travel because you probably haven't been there yet.
Fort Blueblood is a two-level Marauder lair, although you'll probably find something like Imps or Trolls actually guarding the father's coffin. The coffin, wouldn't you know, is on the second level at the very back and you can't open the porcullis to the shortcut route from where you are. Blueblood is a pretty straightforward dungeon crawl with decent loot along the way. Bring along some good Feather potions or spell effects because, depending on your level, you'll probably pick up a sizeable haul of weapons and armor and I'd hate for you to have to make two or three trips. After you pick up the amulet, who should show up but Kalthar. He's not happy that you've put a spoke in his wheels by picking up the second amulet and lays into you. He's not too tough to take down because the only thing he has is a dagger. Prior to the patch, it was possible to get out without confronting Kalthar (which kind of hosed the quest). With the patch, you have to fight him.
After disposing of Kalthar you can either take the long way back or the short way back. The short way uses the stairs to the right of the bridge ("right" from where you are) and brings you out behind a portcullis that you passed near the entrance on the way in. But since the lever is on your side you couldn't do anything about it earlier. Now you can.
Head back to Leyawiin and give the amulet to Dagail. The visions and voices stop and your recommendation is a done deal.
Skingrad (moderate difficulty, travel required, combat required)
Talk to Adrienne Berene. She's usually up on the second floor. Yet another missing guildmember; Erthor. You should be so lucky to find that it's just a prank. Not this time. Ask around the guildhall and you'll find that no one has seen Erthor in quite a while. Seems that Adrienne more-or-less banished him from the guildhall after that "awful Scamp incident" a while back. Since then, he's set up shop in Bleak Flats cave, but checks in periodically for supplies and whatnot. Except for Druja, who can fill in the location of Bleak Flats Cave on your map, no one else can tell you much more than that. Druja rather pointedly tells you that you should remind Adrienne that the whole thing was Adrienne's idea in the first place. If you do, Adrienne will teach you a Weak Fireball spell, but still expect you to go retrieve the missing mage. Figures.
Bleak Flats is more-or-less northwest of Skingrad and not very hard to get to. You might have an overland encounter or two along the way, but that's about it. Inside the cave you'll find a lot of Deranged Zombies (perhaps Erthor should give up Conjuration and take up knitting - at least a dropped stitch won't try to take your head off) and you'll have to get rid of all of them before Erthor will leave his hidey-hole at the back of the cave. Once all seven or so of the zombies are Mort Flesh, you can either send him back to Skingrad on his own or have him follow you. If you send him back on his own, it will take most of a day before he actually gets there.
Cheaters take note: while the quest stage of getting Erthor back to Skingrad is active, Erthor is considered a critical NPC and can't be killed. So you can take him along on all sorts of adventures and let him be the cannon fodder since all he'll do is go unconscious for a little while. He's not very good in a fight, but because his Stealth skill stinks (he's a mage, remember?), he can't hide and is a natural-born monster magnet. They beat on him, you beat on them. What could be simpler? And everyone's happy (except Erthor, of course, but he's unconsious and won't be complaining).
Otherwise, get him back to Adrienne. After they talk, she'll promise to send along your recommendation when she has a free moment.