Neverwinter Nights was already suggested. If you still have it, I suggest you check out PW Action for Multiplayer and go to Neversummer 4. All in all, I loved the story line for NWN games, as I've beaten Hordes of the Underdark, Neverwinter Nights 2, and Mask of the Betrayer.
But when I play single player, I always get pissed at the single player gameplay. Like getting killed by one single spell, or other things that make the game grossly unfair like the End Boss of HoD who is immune to all magic, immune to all elemental damage, and 20 physical damage resistance. Killing him took forever, and felt like a waste of time.
Neversummer 4 has been modified for nearly four years straight and it finally left Beta this year, I seriously suggest checking the server out.
Also, for a good old-school Strategy Game, Age of Empires II. Out of Age of Empires I, Age of Empires II, and Age of Mythology, this one was my favorite. The Map Editor is insanely easy to use, and leaves the game with endless possibilities of different kind of gameplay. Unfortunately, Zone closed down CD-Rom Multiplayer in June 2006, so you'll have to go to IGZones for Multiplayer on Age of Empires II.