A good multiplayer mod while you wait for Bioshock!
If you guys like Bioshock check out this mod for Unreal Tournament 99.
It's a stealth action FPS game and it has an editor included with every copy of UT 99. (Which goes for pennies on the dollar in Ebay)
It has a small community. The objective of the game is to play as a Thief or Guard. Thieves break into places and take away loot while completing objectives.
Guards try to prevent the thieves with a variety of tools and traps. The Artifically Intelligence is well done as well. Custom voices, textures, and maps are found in the mod.
Thievery is based off of the Thief games of PC which are based off System Shock which is what Bioshock is based off of. Confusing yes but they're all related!