I dont understand why everyone thinks Halo is the best fps ever. Sure the graphics look great but the story was ok and there wasnt enough varying environments(levels). It felt boring because the a majority of the levels were really similar.
Games to go with the Xbox:
Halo(I dont think its that good), Splinter Cell, Dead of Alive 3, Panzer Dragoon Orta if you like shooting games. I know Im missing something here...
Gamecube:
Mario Sunshine(if you like platform stuff), Metroid Prime, Super Monkey Ball, maybe even Mario Party 4 if you got buddies to play with, Super Smash Brothers Melee.
Ps2
Grand Theft Auto 3: Vice City, Tekken 4, Devil May Cry, Lord of the Rings: The Two Towers(if you like beat'em ups, not sure if they are out yet for xbox or gc they might be), Grand Turismo 3: A-spec (driving game).