First Person Shooters:
Killzone 2 (3 is coming out soon)
MAG
Brink
Battlefield Bad Company 2
Call of Duty: Modern Warfare 2 (Black Ops is coming out this fall)
Borderlands (buying the expansion packs is a must)
Crysis 2 (coming out soon)

Third Person Shooters:
Socom 4 (coming out soon)
Uncharted 2
The latest Ratchet and Clack

RPGs:
Final Fantasy 13
Fallout 3: Game of the Year Edition (Fallout New Vegas is coming this fall)
Grand Theft Auto 4
Red Dead Redemption
Assassin's Creed 2 (third one coming out soon)

Racing:
Blur
Split Second
Grand Turismo
ModNation Racers

Rhythm games:
Dj Hero 2
the Latest Guitar Hero
Rock Band 3 (coming out)

Platform:
Littlebigplanet 2 (coming out soon)