Games that should be given a try:

Resistance: Fall of Man
Heavenly Sword (Sorta like a God of War game with a female lead)
Uncharted: Drakes Fortune (if you like a mix of Tomb Raider and Indiana Jones movies)
Gran Turismo 5 - This is going to be a damn good racer from what I've experienced with the Prologue
Metal Gear Solid 4 - I know you said it already, but it needs to be said again cause it's going to be that damn good
MLB 08 The Show - If you like baseball, Road To The Show is very addicting.
White Knight Chronicles
Resistance 2
Mercenaries 2: World in Flames
Civilization Revolutions - if you like Turn Based Strategy


I've heard a rumor that Konami might release Suikoden on the PS Store; the rumor was that the ESRB re-rated it for the PS Store and the PSP.