Either Syphon Filter- great shooters with surprisingly good controls
Valkyrie Profile: Lenneth is a great non traditional JRPG remake of the original PS1 game
Metal Gear Solid: Portable Ops- it's Metal Gear; 'nuff said.
Puzzle Quest- incredibly addicting RPG version of Bejeweled. Sounds corny, but it's oh so fun. No way I'd play Bejeweled otherwise.
Wipeout has a ton of great arcade racing action
My Top 5:
Shadow of the Colossus, Metal Gear Solid 3, Shenmue, Skies of Arcadia, Chrono Trigger
My 2 nex-gen systems: PS3 
and Wii 
Prediction Aug '08: We see the PSP2 released fall '09. Graphically, it's basically the same as the current system. UMD drive ditched and replaced by 4-8gb on board flash memory. Other upgrades: 2nd analog nub, touchscreen, blutooth, motion sensor. Design: Flip-style or slider. Size: Think Iphone. Cost: $199. Will be profitable on day 1.
