I love me some b&d. Shit, I mean bd&d.
I bought the Holy Grail of old-school Dungeons & Dragons from eBay and it arrived today: the Rules Cyclopedia. If it were a woman, I would make love to its smooth brown cover and creamy white pages. It's a hardcover, 300-page compendium of all the material from the D&D Basic, Expert, Companion, and Master sets with some extras thrown in, like the Mystic class (a Monk class which is, funnily enough, better than the 3e Monk), and full-color maps of Mystara.
You could run a campaign from 1st to 36th level with nothing besides this book.
There are rules for adding fine wood floors to your fortress or stronghold!!!
Someday, I will run a campaign with this sucker. Water weirds, ahoy!