Buy Fallout 3.
I saw the teaser for Bioshock 2 the other day. It came an unlockable on the PS3 port of Bioshock, which kind of made me nervous at first, I'd really hate to see that game become a PS3 exclusive. Best I can tell no details about the game beyond what is given in the teaser have been released. I really hope that thing will be a 360 title.