Here's my favorites (in no real order):
1. Warhammer Quest. It's the best hands down. It's easy to play, doesn't take itself seriously, and deadly as hell. Surviving level by level in WQ is a badge of honor.
2. Castle Ravenloft. Quick and easy to play dungeons with rules that are by and large already familiar. If a robust campaign option ever came out for this (and the other D&D boardgames), I'd likely play this instead of D&D in a heartbeat.
3. Hero Quest. This is the game that got me into RPG's many years ago. It still gets pulled out from time to time.
4. Descent. I wish this one played quicker. It could easily be my favorite. Road to Legend makes it easier to digest, but it's still a game that I'm the only one that wants to play it.
5. Dungeons and Dragons the Boardgame. It took me a while to get my hand on this and the two expansions, and while it's mostly just a reskinning of Hero Quest with more options, it's still enjoyable, just not as much as the other games on the list.
6. Dungeon. I still bring this out from time to time and it'll likely be one of the first games I pull out of the stack when/if my son becomes interested in gaming. It's pretty simplistic, but that's part of it's charm.
7. DungeonQuest. A race against time in dungeons so deadly that they can make some WQ adventures look like a cakewalk. I picked up the new edition by FFG, and it's still deadly as hell. It's a lot of fun, but if you're someone that doesn't like games in which the game wins most of the time, pass on by.
8. Drakon. This is an easy to play hard to master dungeon crawler. The players lay out the dungeon room by room. Rooms have different effects, both good and bad. The goal is to be the first player to collect 10 coins to win. It's really easy to play and it plays really quick as well.
9. Dark World. This is a goofy little dungeon crawler that came out around the time of Hero Quest's peak in popularity. It's not a good game that relies heavily on gimmicky props. The monster minis are cool, and worth the price of finding a cheap copy. The rest of the game is pretty forgettable.
10. Mutant Chronicles: Siege of the Citadel. It's sci-fi and plays similar to HQ. The stats for players and monsters don't match up very well, making some monsters virtually impossible to kill. Get passed that, and it's a solid, classic crawler that can still be found at a decent price.
