Flower is an absolute must! Screw all the other games, Flower should be your nr. 1 priority! It's beauty and the poetry it uses it to portray is amazing, and I don't even like poetry! Trust me, this is one to get!
LittleBigPlanet is a blast in local play, it really is fun like few games can give you.
I would also recommend Demon's Souls, although I have never laid my hands on a copy of it... *sigh*
And since you don't have your collection up, I'll just further tell which games I can recommend (exclusives and multiplat):
Batman: Arkham Asylum
inFamous
Ratchet & Clank Future: Tools of Destruction (and get Quest for Booty if you liked ToD)
Ninja Gaiden Sigma 2 (playing through this right now, if you don't already have NG2, I can certainly recommend it)
Valkyria Chronicles (some terrific tactical gameplay, a nice twist on your typical SRPG)
Resistance 2 (only for the coop though, but that is quite good!)
PixelJunk Monsters (like with LBP, this needs to be played with a good friend, it's a great coop game!)
I also recommend looking out for PixelJunk Shooter, it seems like another great PixelJunk game: http://kotaku.com/5371291/pixeljunk-shooter-impressions-an-improving-flow







