This thread is about all the Great PSP games small and Large alike, I'll start with my recommendations...
Gundam vs. Gundem Next Plus (there's a translation floating around)
Great game!, its accually better than the Dynasty warrior gundam games, plus it's got Gundam Unicorn!
Phantasy Star Portable 2 + Infinity (coming soon)
PSP2 is a must have if you won a PSP, this game has sooo much content, and its really fun to boot.
Infinity just breaks the scale adding over twice as much content to the original, Can't wait for the US release
Dracula X chronicles
a 2.5d Remake with a bit of new content, plus the original game AND an updated version of it's sequel, AND a bonus peke (pc engine, wrong chip minigame)
this game is proclaimed as the Orange Box of PSP.
Blazblue Continuum Shift 2
throw a Console game on the handheld, Give it all its DLC, and put in a few new modes and top it off with online play, pure win.
Gallery mode also has original peices and a few hints toward a 2.5D (like SFIV) BB3
Guilty Gear XX Accent Core Plus
its the latest GG with new features, nuff said.
Tekken Dark Ressurection
This was so popular it got a PS3 release, that alone stands for something.
Final Fantasy - ALL PSP releases
If Final Fantasy Sucks for you, you're probably still looking at console releases, the PSP has the best FF games as of late.
not to mention type 0. Holy Shit. I played the Demo and was blown away.
Persona 3 Portable
Part Life Sim, Part RPG. this game is renowned one of the best RPGs of all time, I agree.
Kingdom Hearts Birth by Sleep.
Sure KH is getting to a Milking point in the franchise, but this game is both Fun and challenging, also great for people who want KH to take itself a little more serious plot-wise.
Metal Gear Solid Peace Walker.
Venture with Big Boss with the next best MGS, Honestly, this is way better than MGS4. with super high replay value.
that's it for me...