snowkatt: final fantasy 6 7 8 and 9
corpse party is also worth looking in to
ridge racer type 4 as well
I would anti-recommend FF7: It's a horrible game.
On the other hand, FF5 is really good, but I don't know how the PS1 version plays on the PSP. (That version, which is probably the worst (non-smartphone) version of the game (they messed up the audio), had a problem that would corrupt the display when trying to save on a PS2, and apparently would even crash on a PS3.)
FF4 is also good; the PSX version is, of all the official English versions, the closest to the original version in terms of gameplay, difficulty, and game balance.
mrkgnao: Vagrant Story
Parasite Eve 1 and 2
Final Fantasy Tactics
Tactics Ogre
Hoshigami: Ruining Blue Earth
Final Fantasy 7 and 8
Legend of Dragoon
Again, I would anti-recommend FF7. (I haven't played FF8 except the PC demo, but it seems to have many of the same problems.)