Bah, took my options away..but hey will give them again.
If you can find them Kingdom Hearts is decent, and KHII does improve on the first a lot. I have the japanese one, Final Mix + which adds more to the game, so yeah, i do think it is good.
Erm, Persona 3: FES and Persona 4 are brilliant games that i'd recommend you pick up if you want PS2 RPG's. Both are brilliant games. The story for both is extremely engrossing, battle systems are great and it can take the better part of what...120 hours to complete all of Persona 3: FES(thats both the original game, 3[called the journey] and FES[The Answer]) and probably about 80 or so for P4. This isn't including the new game + bit either.
Erm..other RPGs...I had a couple more i was going to mention, but i'll have to get back to you on them. FFX and XII are worth playing. I enjoyed XII, but it just never came across as good as it could have been. Apparently there was an international version made for japan which adds to it, but we won't ever see it i expect, so thats kind of disappointing, but still, it can take a good while to play, there is tonnes to do in it.
AH, Disgaea. I'm not entirely sure if you'd classify it as a full on RPG, but that maybe worth looking into as well. 1 + 2 are on the PS2, and have/are getting a re-release on the PSP with more added to them as well.