Well it seems you like Bethesda and Bioware games, so first off all you should add Bioware's Mass Effect to your list, but also if you missed any you could try some of the last gen titles like Morrowind, Star Wars: Knights of the Old Republic, or Jade Empire.
Otherwise these are AAA titles that Bethesda and Bioware specifically specialize in, so unlike a FPS there you aren't going to find a lot of alternative options. Unless you go to PC games where these RPG's you like are far more common, with lesser but still good titles like The Witcher, Risen, Neverwinter Nights 1 or 2, and so on.
I echo the Mass Effect 1 & 2. And if you don't mind last gen games, you can play the X-Box games Star Wars: Knights of the Old Repubic 1 & 2, and Jade Empire on the 360. Fantastic Western RPG's like Fallout, Dragon Age, and Oblivion, and being older game, should be able to get them for a fantastic price.