Most of these games have demos on the PS Store, so it'd be a good idea to try them out first.
Motorstorm is pretty good. Lacks splitscreen, but the core racing is brilliant.
Burnout Paradise is also good, although the open world design is a bit polarising. The crashes are second to none.
Super Stardust HD or Everyday Shooter, if you're into the Asteroids style of gameplay.
Warhawk is great, but online only.
Ratchet and Clank is damn good, but lacks the online modes from earlier R&C's
Try getting a few mods for UT3 as well, it really extended the lifespan on that game for me.