Never tried Uncharted myself, but a lot of people seem to like it. You are already getting MGS4 which is probably one of the best games out there for the PS3 at the moment.
Try Deadspace, good Thriller/Horror game, awesome atmosphere.
You'll definitly want to get InFamous (or Prototype, haven't played the latter one though, but a lot of people seem to like it as well).
GTA4 if you didn't try it on the PC.
Call of Duty 4, although 'old', it is still a blast to play online.
Try out some demo's on the Playstation Network Store.