I strongly second the suggestion of Planescape: Torment and the Icewind Dale games. However, there are a ton of other D&D games out there, depending on your tastes...
If you don't mind old school graphics, and if your machine can run DOS (or a DOS emulator), all the old goldbox games are still out there:
Pool or Radiance (original)
Curse of the Azure Bonds
Pools of Darkness
The Dark Sun games, used a different interface, and were really fun:
Dark Sun: Shattered Lands
Dark Sun: Wake of the Ravager
Also be sure to check out Forgotten Realms: Unlimited Adventures
This is sort of the predecessor to NWN. It allowed anybody to make their own "goldbox-style" games. The game had a huge support community for years and years. I think it's dwindled a little since the arrival of NWN, but there are still tons of modules online for it.
The Eye of the Beholder series uses a fixed first person view and is mostly a dungeon crawl. If you like this interface and just want to kill some time killing monsters, find Dungeon Hack, which randomly generated dungeons for you to plow through using the Eye of the Beholder interface.
Yes, the graphics in all these games are archaic, and it can be a challenge getting some of them to run on today's machines. But a lot of it is still solid, fun D&D.
And the best part is that most of these games can be found really cheap, some even free.
Carl