Well, everyone knows that the best games you can get for the PSP are Pandora's Battery and Dark Alex, as far as cost vs replay value.
I think, it really depends on what type of games you like. Maybe, Patapon or LocoRoco would interest you. Personaly, if I were going to buy a game in the same vein, I'd get World Of Goo or Spirit Bubbles 1st, but that's just me. A safe bet would be to, look at the list of top sellers and highest rated games and look into the ones that catch your eye. Research those a little further(demos, wiki, game sites, youtube videos, that sort of thing), to narrow it down and take it from there. I'm sure you know what you like, better than some random ppl on vg.
If you like old school RPG's Falcom games and Star Ocean are worth looking into, even though PS fans seem to discount the SO series, now that part 4 is coming out on the 360.
