Uncharted [rent] is a must. Beatable in 12 hours but still has a lot of replay value, but seeing at the sequel is just in 2 1/2 months, I would just rent it.
Uncharted 2 is a MUST BUY.
Valkyria Chronicles - If you want an RPG game before FF13, this is a good one.
Tales of Vesperia - Another good RPG to get before FF13. Coming in Japan Oct 09, not sure about America.
Call of Duty 4 - Must have game, got it like 3 weeks ago for free, and played 40 hours on Online alone.
Ratchet and Clank - Fun platforming game that you can easily pick up and play anytime.
inFamous - FUN, ADDICTIVE GAME.
Before buying these games though, try out the demos. The demo for Valkyria Chronicles is somewhat really short, the story is good though, and gameplay when it gets into more in depth.
Oh yeah, also, you should get some PlayStation Network games. The ones you should get are SuperStardust HD, Bionic Commando, PixelJunk Eden, PixelJunk Monsters, and Fat Princess [not out yet]. Before buying remember, to read reviews if you are not sure about getting them, and even trying out the demos if you'd like to.
Battlefield Bad Company 2 > Modern Warfare 2
