Boaderlands is coming out this fall for consol and PC. It's looking OUTSTANDING. It has visual elements that make a post apocalyptic landscape look outstanding, something that Fallout 3 is lacking and it includes 4 player Coop but I'm not sure if that is multiplayer or it is coop in the solo story (if there is one). It received a cover story in the June 09 PCGamer. I'm excited about this game! 
From the Borderlands FAQ:
What is Borderlands?
Borderlands is an upcoming sci-fi FPS game with 4-player co-op. It has RPG elements and boasts half a million weapons.
What platforms will Borderlands be available on?
PC, XBOX 360, and PS3
From the Borderlands FAQ:
What is Borderlands?
Borderlands is an upcoming sci-fi FPS game with 4-player co-op. It has RPG elements and boasts half a million weapons.
What platforms will Borderlands be available on?
PC, XBOX 360, and PS3