I finished Dark Spire for the DS (all three endings) and I'll soon be trying to beat Might and Magic 1. I've discovered I love these games. I'd like to hear about more complex games like might and magic 6 where the enviroment is fully 3D. But what I'm really after are games in which you only move one block at a time and you have to create your own map.
Can you recommend any good ones? I've heard of an old one called Eye of the Beholder--is that worth tracking down? I love games with a steep difficulty curve and puzzles in the dungeons. A game with lots and lots of flavor text if one exists. Some humor doesn't hurt either.

Get Etrian Odyssey 1 and 2 on DS if you like charting your own maps.

EotB is great if You don't mind/like AD&D.
I'd strongly recommend playing the classic Lands Of Lore: Throne Of Chaos if You haven't already. Great game. While not technically a 100% crawler (frankly, i'm not sure if EotB is a pure DC anyway), it bears many similatities to EotB, mostly because, Westwood Studios, creators of the first two EotB games were not given the rights to create EotB3, so they created somerthing of their own. ;)
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There's also the late addition to the genre, dubbed "the last 2,5, stepped RPG", called Anvil Of Dawn. Though it's made by 3DO [creators of the M&M series], so don't expect wonderful gfx.;P
Also, there's this almost unknown M&M clone, called Yendorian Tales [the second and third game is FPP].
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I love Might & Magic 3-5, but they're automapping. Ditto Thunderscape, SSI's overlooked fantasy steampunk crawler (though I don't know if you can get it running in Dosbox - I had problems with it last time I tried).
Wizardry VI: Bane of the Cosmic Forge is pretty awesome. Bring your graph paper for that one.
All of these games include some puzzles and riddles, and Bane of the Cosmic Forge is fairly challenging, if only because it tends to be unfair. Bane is also the most puzzly, with a lot of adventure-style inventory puzzles to work out. Of the ones I listed, it's probably the one that best suits you.
It's been a very long time since I played Eye of the Beholder, and I never finished it, but I remember it being a solid game. It uses AD&D rules, if that matters to you.

I'm actually a few levels into Etrian Odyssey 2 (I haven't seen 1 yet). It's good except for the item gathering aspect of the game. I have one group of high powered adventurers and another party of slaves whose sole function is to make money. It feels like a classic RPG... with some MMORPG node farming thrown in. But I think I'll finish it, anyway! I love the classes.

Oh yes. This and it's sequels are some of the only games that if they ever managed to turn up on GOG, I'd buy in an instant.

EoB 1&2 are very good. I played 1 pretty much when I was younger and it was a new game. I could beat that bastard on one sitting.
Lands of Lore is also good. The first one I mean.
And never forget Dungeon Master 1. 2 is okay too. If you can and want a real challenge, track down Chaos strikes back.

Neverwinter nights.

Oh, oh!
Akalabeth: World of Doom if You want to be hardcore, and of course Ultima Underworld 1&2, but UU doesn't feature the step-by-step/90deg movement.
I must point out that the aforementioned Lands of Lore, as well as Ultima Underworld and Yendorian Tales, all feature automapping. But You don't have to look at the map, right? ;D
[edit: Shame on me, i forgot about one!]
And last, but not least, The King, The Queen And The Jester, features awesome pixelated GFX, loads of pressure plate puzzling, step by step movement, 90 degrees rotation, and again, viewing the automap is optional.
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M&M II-III-IV-V
Mapping 3D crawlers on graph paper is annoying as hell.

Not to me, I like having those finished hard copy maps. In dark spire you do you the option of an automapper but I found it easier to look at my hand-drawn map then flip back and forth from the game to the map screen. I also learn the map better when I draw it, so I don't have to look at it at all as often.

Ravenloft: Strahd's Possession & Ravenloft: Stone Prophet are supposed to be good.
People tend to be a little divided on the combat system of this one, but the Ishar series is available here on GOG. 4 games for $5.99 isn't bad at all, and not too large a risk. It seems very old-school though. (A turn-off for some.)

One of my favorite dungeon crawlers is Shining in the darkness. Great game for the MegaDrive (Genesis if you are from US). The time before JRPG turned to shit;) (only half kidding)
The Darkspire and Etrian Odyssey 1 & 2 are also great games, the third one is coming soon to.

I don't have a favorite... I love them all ! Currently playing Wizards & Warriors.