Shin Megami Tensei Nocturne
Digital Devil Saga 1 and 2
Wild ARMs 3
Yakuza 1 and 2
Xenosaga. Gameplay sucks, but story, world, and XenoCard are worth playing through this game for. Or just Youtube the story.
Scarface the World is Yours
Cnampions of Norrath. Good Diablo Clone
Champions Return to Arms
Dirge of Cerberus
Dragon Ball Z Budokai Tenkaichi 3
Taito Legends 1 and 2
Castlevania Lament of Innocence
Devil May Cry 3 Special Edition
I'd also recommend the Armored Core games if you're a fan of them. Try out Armored Core 2 and 3. If you like them, get the rest. The earlier games are better than the PS3 games.