JudasIscariot: Don't forget about Persona 1 and Persona 2: Innocent Sin, which was just released not too long ago.
evilguy12: They worth playing? I am thinking about getting P2 but I heard it has an annoyingly high encounter rate and a slow battle system.
The first one, SMT:Persona, plays sort of like an Eye of the Beholder dungeon crawler (first-person view, 90 degree turn angle etc.) and has you walking around on a map[ of sorts. The encounter rate for that one varies but you can negate battles by talking to the demons and basically getting them to leave but you get no XP from that.
Innocent Sin plays somewhat similarly but also introduces the "Rumor" mechanic where you can, via rumormongering, change the equipment a shop carries and other things.
Also, Eternal Punishment, the second half of Persona 2, is getting an English-language PSP port due out sometime in May of this year.
Both games are fun but the first one, Persona, may take some time to get into after P3 Portable.
Innocent Sin also features a second story line (the Snow Queen quest) and a secret recruitable character that requires a bit of a guide in order to fulfill the requirements to get him.