You should definitely look into buying Tekken Dark Resurrection. I don't really need to say why. Its Tekken as it should be, not some gimped version like the GBA one.

Patapon is also a must buy. There's no other game like it and its at a budget price. Nothing much else I need to say.

Wipeout Pulse is also fantastic. Really fast, full of features and a good soundtrack. Its got online multiplayer too.

Other stuff you should look into is Jeanne D'Arc, God of War, Metal Gear Portable Ops, Street Fighter Alpha 3 Max and Daxter.