You can't go wrong with: Baldur's Gate, Baldur's Gate II (my personal all time fav), Morrowind (excellent, but big, really big), and Knights Of The Old Republic (pc version of course. probably my all time second fav). Then lets not forget Fallout and Fallout II.
I also enjoyed The Temple of Elemental Evil (despite all the griping I've read about it). Neverwinter Nights isn't all that bad either, especially if you find some good user made modules.