The Dungeon Alphabet by Michael Curtis (designer of Stonehell Mega-dungeon) is a fun and informative book that would be worth twice the listed price. Its forty-eight pages long, comes in hardcover only and is published by Goodman Games (http://www.goodman-games.com/). There is wonderful art though out the entire book, almost every page is illustrated with beautiful black and white images created by the likes of Jeff Easley, Erol Otus, Stefan Poag, Jim Roslof and a number of others.
Every letter of the alphabet is given a meaning, always relating to dungeons. A is alters, B is for books, C is for caves, etc. Flip to the according page and you will find a short paragraph on each subject followed by a table of random versions of that item. For example, H is for hallways so when you flip to the hallways page there is a list of twenty random hallway descriptions, each different and varied.
What I love about this book is not just that you get all kinds of fun tables and charts to roll on, it really ignites your imagination and gives you so many ideas and suggestions that can make your dungeon unique and varied.
For $9.99 this book is a steal, I had a very enjoyable time reading through it, I found it both fun and useful. The book is written so that it's system free, it can easily be plugged into any retro system of your choosing. Unfortunately it seems to be out of print, the copy I purchased from Amazon was at the list price, but all the copies left seem to be way above that. If you can find it cheap, pick up a copy, its a great read and great addition to any DM's toolbox.