Blood of the Daedra
If you pursue the various conversation topics with Martin, you'll learn that Mankor Cameron somehow bound himself to the Mysterium Xarxes in order to create his pocket paradise. Martin thinks that he can do this, too, but will need some ingredients to complete the binding ritual so he can open a way into the paradise. The first one that he has been able to figure out is Blood of the Daedra, which he takes to mean that he needs a daedric artifact of some kind.
It really doesn't matter which one, any old daedric artifact will do. If you have not already read it somewhere else, pick up the copy of "Modern Heretics: A Study of Daedra Worship in the Empire" from the table in front of Martin (don't actually take it - just pick it up and read it). It's not going to tell you anything earth-shaking, but it will add the "Daedric Cults" conversation topic to several NPCs and mark the location of Azura's Shrine on your map if it isn't already there.
Here's the tricky part - all of the daedric artifacts are useful to a greater or lesser degree, depending upon your playing style. The question is which one will be least useful to you because you're going to permanently lose the artifact. The reason that Azura's Shrine gets marked on your map is probably two-fold: it's the artifact with the lowest level requirement (you have to be 2nd level before Azura will talk to you) and it's the artifact whose effect is most easily duplicated (it's a soul gem - a reusabale one, but still just a soul gem). However, if your character creates and uses magic items that need to be recharged, Azura's Star might be very useful to you, so a different one might be in order. My personal choice would be Wabbajack - it's a fun artifact and available almost from the beginning of the game, but its utility is questionable.
So here's a quick rundown on the artifacts that are available to you, their level requirements and my thoughts:
|Azura||Azura's Star||2||Reusable Soul Gem - a potentially useful, but not critical artifact|
|Sheogorath||Wabbajack||2||a staff that changes critters into something else; fun, but risky|
|Namira||Ring of Namira||5||Reflect Spell and Reflect Damage - very nice effects that can be duplicated|
|Vaermina||Skull of Corruption||5||creates a temporary (30 seconds) "evil twin" of whatever you strike; makes creatures into their own worst enemy; can be a lot of fun|
|Malacath||Volendrung||10||Warhammer with Paralyze and Drain Health effects - can be duplicated|
|Meridia||Ring of Khajiiti||10||Chameleon and Fortify Speed effect - handy for sneaky-types|
|Nocturnal||Skeleton Key||10||Unbreakable lockpick and +40 Security skill boost - very handy for anyone|
|Peryite||Spell Breaker||10||Shield with Reflect Spell effect - can be duplicated|
|Mephala||Ebony Blade||15||Dagger with Silence and Absorb Health effects - can be duplicated|
|Hircine||Savior's Hide||17||Light Armor Cuirass with Resist Magic enchantment - not too useful for tanks|
|Molag Bal||Mace of Molag Bal||17||Mace with Absorb Magicka and Absorb Strength effects - very nice effects, but can be duplicated|
|Boethia||Goldbrand||20||sword does 22 points of fire damage per strike - mm-mm toasty|
|Clavicus Vile||Masque of Clavicus Vile||20||Boosts personality 20 points - useful, but not critical|
|Hermaeus Mora||Oghma Infinium||**||one-time attribute and skill boosts - DO NOT GIVE THIS TO MARTIN|
The reason that there is no level requirement for Hermaeus Mora is that there isn't one. The requirement is that you complete all of the other Daedric quests (which effectively means "Level 20 or higher") and have this quest active. However, you do NOT want to give the Oghma Infinium to Martin. Being a one-shot permanent 10-point boost to one or two attributes and three or four skills, depending on your choices, it's the most useful of the artifacts regardless of your class and playing style. If you get to this point and the Oghma is the only artifact available to you, reload an earier saved game.