Halo. Call of Duty.
Also, Gears of War. I have BOUGHT the first one used, but never played it.
Counterstike, I guess I have technically played, but I hate the game with a passion because it single-handed destroyed Tekworld's (computer gameroom we hung out at) variety of Duke Nukem 3D, Starcraft, Diablo, Warcraft 2, Quake, and replaced it with mindless drones that played Counterstrike over and over again. I hate realistic weapons in FPSs. Hell, I came back two years later, and the fuckers were STILL playing Counterstrike 24/7!
As far as the games listed above, highly highly highly recommend Mass Effect. Everybody is playing ME2 right now. Also, I've only played one Racket and Crank, but it was a damn fun game. I wish that the newest one wasn't PS3 only.
Rosalina: But you didn't.
Robert: But I DON'T.
Rosalina: You sure that's right?
Robert: I was going to HAVE told you they'd come?
Rosalina: No.
Robert: The subjunctive?
Rosalina: That's not the subjunctive.
Robert: I don't think the syntax has been invented yet.
Rosalina: It would have had to have had been.
Robert: Had to have...had...been? That can't be right.