The general sentiment is that Valkyria Chronicles and Demon's Souls are the best RPGs on the PS3. The former revolutionized the SRPG and the latter is a really awesome, really creepy, action RPG with a very old school vibe to it. As Wolf stated, the story in Valkyria Chronicles is kind of slow in the beginning, but the gameplay is absolutely excellent and the narrative does suck you in eventually.

Of course, you could never go wrong with Disgaea games. It seems like you know what you're paying for, and from what I've heard they've been just as great as the older ones.

White Knight Chronicles is one of the most classic RPGs you could find on the system. You explore towns, talk to people, buy stuff from shops, pick up side quests, explore environments, and fight baddies. The plot is very typical JRPG stuff, but it never really pushes the envelop or make you think it's a great story. Also, the fighting/exploring can drag on a bit long towards the end of the game. The customization is excellent, though, so the combat can be a lot of fun when paced properly. One of the big draws is the online multiplayer, which lets you take your custom character online, meet other players in their custom-built towns and do side quests with them (or a friend). I had an awesome time playing some of them. The only problem is there's only a few starting out, you're not really high enough level for the bulk of them until the end of the game and by that point you might be tired of the combat. But the ability to make your own town (called Georama) makes it pretty addicting. It's easy to make the basic stuff, but to really expand it and make it a really cool place, you have to get out there and forage for the slightly more uncommon items from resources and enemies. It's actually really cool and gets you charged to get out there and play. So White Knight Chronicles is a mixed bag, but for any fan of traditional RPGs who has a PS3, I would say it's a must have.

This may not be what you want to hear, but the PlayStation Store available through PSN on PSP/PS3 is growing to be a very nice resource for RPGs. I've beaten Final Fantasy VII and Xenogears, and have files on FFVIII and FFTactics as well, which each are only $9.99. I also want to check out Arc the Lad, a really cool PSOne SRPG series, which are only about $5-10. I know they're PSOne classics, and from what you've said you probably own a lot of these games already, but it's a really awesome resource for what you've missed. Whoever works at Sony/Square Enix for putting content up there must be a huge RPG nerd because there's a lot of awesome stuff from Square up there.

Lastly, I haven't talked about FFXIII and I really won't say much about it. If you're a FF fan, you have to play it, and hell, you might actually like it. A lot of us on here did, as did I. But I would go with some of the other games first because they're actually really good.