I can't recommend Resistance: Fall of Man enough. It's old, and a bit dated, and the online is now extremely dead. But the campaign is very, very original and fun. Probably my favourite FPS campaign outside of Half Life. The sequels are fun as well, campaigns are solid but the online for them, imo is severely lacking. Fall of Man in it's prime was just outstanding for multiplayer.
Uncharted 1,2 and 3 as everyone said. Incredible games.
God of War collections, and God of War 3.
Trine 2 (from the Playstation store) is just amazing, although I'd recommend getting it on PC of you rather than console.
I'd hugely advise AGAINST Bethesda games on PS3. Fallout 3 and Skyrim are still bugged to hell and Skyrim is near unplayable for big save files.
Final Fantasy XIII, not many liked it but I loved it. It looks much better of PS3 than Xbox as well.
Little Big Planet can be picked up cheap and is very very good fun, so is the sequel.