For me the great games were:
Dungeon Master - one of the first games I had on my PC. Was tough as hell back then (I didn't have the manual), not much easier later on. I still have the ugly photocopied bootleg walkthrough I bought specifically for this game
Eye of the Beholder series - Started not much later, found it much easier and user-friendly in general (I hated the DM magic system, especially since it doubled as a copy protection). Eventually finished the first two games in the series.
Dungeon Master II: Legend of Skullkeep - this game holds a special place in my heart as it was the first game I ran after I bought a sound card. Suddenly the silence, beeps and boops gave way to excellent music, wind blowing in a forest and creepy monster sounds. I think I had to find my jaw on the floor.
Ultima Underworld: The Stygian Abyss (and Labyrinth of Worlds) Yes, I know they aren't grid-based. Deal with it. The best dungeon crawlers ever and waaay ahead of their time technically - these guys were doing full RPG with dialogue, trading, inventory management with nested containers, flying, bridges, free look before Doom was released!
Also some good ones that I fondly remember:
Perihelion - one of the best games ever when it comes to the mood. I love the music, the setting, the steel-amber palette, etc. Didn't manage to get very far though, again, stupid rune magic system >_<
Black Crypt - played this one with a friend, who was much more of a fan than me. Definitely an interesting game.
And thanks for recommending me some good titles! Having finished Grimrock I have a craving for more dungeon crawlers. For some reason I've never played the first Lands of Lore games (the last one looks like crap, not gonna touch it), I may try again Anvil of Dawn too. The rest goes into a text file I'll try when I get bored.