Elder Scrolls 3 : Morrowind - A classic RPG well designed for single player. Extremely large with decent graphics, you can pretty much do what you want. The exp system is well developed with you receiving exp for carrying out tasks related to your skills (eg a theif gets points for theiving, a wizard for casting spells, a warrior for getting medieval with a axe). There are some complaints about the combat system though as it is not really turnbased, you have to click your mouse.
Divine Divinity - Good RPG if you are not worried about graphics. A cross between Diablo style and Baldurs Gate. The quests are great and there is a good balance between exploration and combat (some amusing voice acting too!). The character development though is a little dated. IMO there were not enough options, besides the starting stats you could essentially create any character you wanted. A lot of the skills were a little bland and dull. However, the game was really about the storyline.
Wizardry 8 - A little long in the tooth, with dated graphics. But this is a serious RPG, It is quite difficult too, with plenty of options to offer a challenge. The character classes are very original and there is plenty to keep you busy, worth a look if you like this series.
Single/Multiplayer (good offline play but seriously enhanced by a net connection) :-
Dungeon Seige - Amazing graphics! This is the bad boy if you want serious eye candy. Gameplay is pretty good too, there is a wide variety of character development and a lot of items to collect. If you have a net connection online play is pretty good, and there is an amazing editor with plenty of add ons.
Never Winter Nights - AD&D, the single player is pretty good, however it loses out on Baldurs Gate 1/2 in that you only control one character. Also the storyline in comparision to those two games sucks! It is far more hack and slash orientated. It does begin to shine in multiplayer though and offers far more depth in terms of character balance and grouping than any other RPG out there. If you have a few mates then definately recommended, other than that I would say that Morrowind or Dungeon Seige is a better bet (depending on whether you like hack + slash).
Online only :-
Anarchy Online - Good Sci Fi online RPG, currently has a 7 day free trial, worth a look.
Everquest - The old skool master, plenty of fun to be had however the graphics are beginning to show their age. Not recommended if you like Player Vs Player combat though as the classes are a little unbalanced in that respect.
Dark Ages of Camelot - Good online RPG, borrows a little from all. Worth a look if you enjoy PVP combat, large scale battles and seiges are a unique selling point.
These are a few current RPGs, if you haven't played classics like Baldurs Gate 2 or Diablo 2, I would recommend you look at these for cheap thrills. The nice thing about the RPG genre is that gameplay is always over graphics. I would recommend any of the above for a play.
NOTE : I did not go into much detail on the online games as these are horrendously huge and really require experience playing. On the online front it is also being aware of Star Wars Galaxies which should be every Jedi's dream
If you want to know anymore, post what type of RPG you are interested in (hack n slash vs storyline?) and I can narrow down the search