For me:
PS2: Final Fantasy X
X-Box: Halo
Gamecube: Metroid Prime
PS1: Metal Gear Solid
Game Boy Color: Tetris
Game Boy Advance: Super Dodgeball
Dreamcast: Soul Calibur
N64: Donkey Kong 64
PC (no, the Mac!): Baldur's Gate II
Close seconds:
PS2: Gran Tourismo--A-Spec
X-Box: Morrowind
Gamecube: Zelda--Windwaker
PS1: Xenogears
Game Boy Color: Zelda: Seasons
Game Boy Advance: ChessMaster
Dreamcast: Sonic Adventure
N64: Goldeneye
PC (no, the Mac): Black and White