The dungeon designs of Zelda: A Link to the Past are pretty good, but Zelda: Parallel Worlds (An insanely brutal-but-playable romhack by Euclid) is vastly superior.
Play all the way through it, as tough as it might be. Took me a few weeks to beat it, but the dungeon and overworld map designs are worth studying.
Here are a few of my favorites.
Castle Guardhouse
The first dungeon, which you must do SWORDLESS for the first half on only three hearts. Pretty rough for an intro dungeon, as it's basically on the size scale of a Dark World dungeon in LttP.
Shiek's Hideout
Probably the most sinister dungeon design ever. Seriously, just watch this madness. So many eye lasers. SO MANY. Not to mention disappearing floors, fire bars, blade traps, wallmasters, spike blocks, and dozens of fake cracked walls.
The Parallel Tower
Featuring false doors that appear locked, hidden passages through walls, and a final floor (8F) that splits into two paths and locks the doors behind you, forcing you to re-enter the dungeon several times.
Oh, and there's a light world and dark world version too, for a total of four trips and 32 floors. Fun times.