This thread is great, and I actually joined neogaf because of it! Thanks for a lot of great tips, some of which have added to my collection.
I've been playing dungeon crawlers since the Amiga-days. I was a huge fan of Dungeon Master, and later I played (and loved) Eye of the Beholder I and II a lot, both on Amiga and MSDOS.
I guess some may consider these a bit far fetched, but I'm a bit surprised they haven't been mentioned in this thread (at least I haven't seen them), as they are (imho) genre defining games:
Zork I
Zork is text based, but I think it can be considered a dungeon crawler. If you have doubts, take a look at some of the
great maps 
And if you haven't played any IF-games (Interactive Fiction, i.e. text based), I strongly recommend trying it. Try Frotz (available for most OS), and try some of the many free games.
IFWiki is one good place to start
Daggerfall was one of the first "open world" games, and really change the perspective of what was possible for a game. God knows I spent many hours on that. It's not a 100% dungeon crawler, but there are "instances" of dungeons, with a great turnbased system. Love it!
