Here is a little list of games to look out for on PSN:
Vagrant Story (EU, NA), Wild Arms 1 & 2 (NA), Xenogears (NA), Suikoden (NA), Parasite Eve 1(NA) or 2(EU), Legend of Mana (NA), Grandia (EU, NA), Front Mission 3 (EU, NA), Final Fantasy Tactics (NA), Final Fantasy IX & VIII & VII (EU, NA) VI & V (EU), Arc the lad 1 & 2 & 3 (NA)
These are more action than RPG but still worth mentioning:
Alundra (NA), Blood Omen: Legacy of Kain (NA), Legacy of Kain: Soul Reaver (EU, NA), Legend of Mana (NA), Castlevania SotN (NA).
Non RPG Honorable Mentions:
Silent Hill (NA), Resident Evil 1 (NA) Directiors Cut (EU) 2 & 3(NA), Metal Gear Solid (EU, NA)
Right, there are a ton more games I could probably mention, but that will do for now.
I was going by the Wikipedia List of PSO classics, so some things may have changed since it was last updated.