Well, there are all sorts of different kinds of RPGs to consider.
If you're looking for a sandbox experience (you know, they put you in a free world and say 'have fun!' The Elder Scrolls series would be my top choice. I played Morrowind back on the Xbox, and obviously Oblivion on the 360. I loved Morrowind a lot, but the dated graphics might scare some people away if they've already played Oblivion. Also, the two KOTOR games were excellent, in my opinion. I found the second installment to be a lot easier, but the advanced skills and class options made it a more enjoyable experience for me.
If you're going for a slightly more linear, eastern-style RPG, you can't go wrong with any of the Final Fantasy games. I know some people will disagree with me, but I thought they were all good in their own right. Also, Dragon Quest 8 stole a good chunk of my life, and you could probably find it in a bargain bin for 5 bucks or something, so you can't really lose.
Lastly, if you can manage to get a copy of the original Final Fantasy Tactics, do so. It's a turn-based strategy game, but I'll still include it with the RPGs. And it is incredible.
FF7 is my top. I also loved 9 and 10... tho the rest just dont do it for me. Also All the elder scrolls (daggerfall anyone?*cream*) are quality. The game HerosArms here on armour games is a zelda spin off but its actually REEEELY playable. In fact Zelda series is good, specially the first wuns and ocerina of thyme as well. Mosntors den is good quick rpg action as well. Also... (trails of into the long hours of the night, jibbering away to hiself and making the occasional cup of tea... moo and two please...)
