These are the best books I have come across thus far. More detailed reviews will be posted here, but for now click the links and read the Amazon.com reviews.
This book by Morgan Jones is the definitive tube amplifier book for anyone interested in guitar of hifi amps. It also has an extensive section on basic electronics and how to chose components. If I were to recommend one book to the guitar amp enthusiast it would be this one. There is plenty of information for all levels. If you don't have it, get it.
A Desktop Reference of Hip Vintage Guitar Amps is the perfect book for someone learning how to service and modify their existing amplifier. This book covers all the information about real vintage amplifiers you will need. This book emphasizes Fender and also has Ampeg schematics (over 100 pages). Author, Gerald Webber is also owner of Kendrick Amplifiers, makes of some of the finest Fender reproductions with their own touch. This book is worth every penny.
This book by Tino Zottola is exactly what the title says. I come from a mathematical background and a book this full of theory really drives home the concepts of tube amplifiers. This book contains general schematics for preamplifiers, phase splitters and power amps. Zottola is able to bring real world amps like Marshall and show how they apply his theory to their amps. The appendix contains resistor codes, capacitor codes, wire gauge, tube structures, tube data and musical frequency table. For 15 bucks you can't go wrong, but this book can be hard to get at times so make sure to check availability in advance.