For an RPG, Crisis Core is pretty great, my favourite game on PSP, though it did only take me about 19 hours....{though the lack of jRPGs in your collection thinks this may not be perfect for you} Patapon 2 is also very very good, and if you loved the first, you should try and pick it up. I think games are region free, so if you don't want the PSN version you can probably import it
You may also want to consider some of the PSN classics because they are pretty cheap, and do involve FF VII and VIII.
Motorstorm Arctic Edge is basically just Motorstorm on the PSP, it is what you would expect and good fun.
Something quirky is Pursuit Force Extreme Justice, the main mechanic being jumping between cars. It is a really fun game, though it does have its low points with the on foot sections