So many good JRPG's on the PS2:
Tales of the Abyss
Shadow Hearts (liked 2 the most)
Persona (liked 4 the most)
I might still be missing some :D
Final Fantasy XII, no doubts.
Its more of an action game than an RPG, but Drakengard.
I really liked Dark Cloud and I had a love hate relationship Summoner 1+2
Not an easy choice at all, but I would probably have to go for Wild Arms 4.
Ar Tonelico 2 is also a great game, as mentioned earlier. Fun battle system and Luca is a 10/10 character. Her spiteful dialogue in the Cosmosphere is some of the best, most fun writing that can be found in any RPG.
haven't played this but looks interesting
I liked the dot hack series as well as Final Fantasy 10..although I am not mush into rpgs.