Re: More on dungeon design!
If you want to learn how to design cool dungeons, start playing Dwarf Fortress.
My dungeon crawls have gotten awesome ever since I started fooling around with that game.
To expound on this thought - the game really does make you think about how you'd actually design a fortress, because it puts constraints on you when you play. It forces you to put in workshops, farms, wells, bedrooms, dining rooms, storage rooms, burial chambers, and all sorts of other things that you probably wouldn't consider if you just dreamed one up on your own.
Its easy to come up with the mundane stuff, like walls and moats and drawbridges and keeps and all the rest; but DF forces you to consider numerous details. Its also the gift that keeps on giving - your dwarves will create all sorts of fantastic loot and decoration ideas. You can look at individual wall and floor carvings, for instance. Some are loaded with all kinds of made-up unique history.
Your dwarves will create all sorts of weird legendary objects that will range from everything like wooden barrels or marble chairs to more traditional RPG fare like swords and gauntlets and breastplates and whatnot.
I guarantee it'll add punch to the game when your players come across dozens of interesting tidbits, like the masterwork birchen bed in the golden chamber once used by Baron Urist Nomdastot which has images of the bear Umungosmust Lomuslospu rending helpless goblins during the glory days of the fortress carved into it; especially since they already found the the grisly dungeon chamber where that must have taken place.
I doesn't hurt that it'll provide locations of the remains of deadly traps and levers. Machines that could throw a cage or a crushing stone their way, or flood the place with water or magma, or collapse a section of the cavern... all sorts of nasty things to put the "adventure" in adventuring party.