Little Big Planet - co-op orientated platformer / level-creator.
PixelJunk Monsters - Very fun co-op tower defense.
PixelJunk Eden - beautifiul minimalist 2d platformer. Easily 10+ hours of gameplay.
Uncharted - Definately worth at least a rental if you're a fan of TPS games. Some platforming though the emphasis is on shooting.
Warhawk - Not for everyone, the learning curve will punch you in the face. I'd rent it or pick it up cheap to see if it's up your alley. If it is, join the warhawk league.
Also keep an eye on Fat Princess, which is going to be coming to PSN sometime this spring. 3rd person team-based action / rts goodness with 32 player online.
Demon's Souls Official Thread | Currently playing: Left 4 Dead 2, LittleBigPlanet 2, Magicka
