I'll back up Benjamin's claim of Fallout 2 as my favorite game - I'll never forget how devilishly fun it was to sell my companions off into slavery and try to beat the game addicted to every drug I could find, haha. It's amazingly balanced, so that you can choose to be Mother Teresa or a serial killer (or Ron Jeremy...ewww) and no one path feels gimmicky and undeveloped. It's the closest you will ever get to an "RPG" in the truest sense of the word.
I also would highly suggest Final Fantasy 5, which was never released proper outside of Japan (I think it's available for PS1 now though). Surprisingly, the story really sucks but the combat more than makes up for it. It was the only FF game until that point (and still is, for all I know--I haven't played any of the later ones) where each character could be assigned any class you wanted, and you could switch their class at any time and mix-and-match all the best abilities. It was brilliant and actually made level-grinding a lot of fun, and I don't understand why they don't do this more often. Oh, and the soundtrack kicked ass.
