A little while ago, I bought "Zinn and the Art of Road Bike Maintenance". It's packed with a lot of technical stuff that you probably won't find elsewhere, eg. tightening torques for most threaded fasteners on a bike. The problem is that it is curiously un-engaging, and the illustrations are a bit "Whole Earth Catalog" IMHO.
Park Tools, as others have said, are really good, both in print and on the web.