One of the great things about being a homebrewer today is the breadth and depth of literature that is easily available. The homebrewing books I've read have been nearly all been well-written, well-researched and focused on issues relevant to homebrewers.
How to Brew, by John Palmer. For most homebrewers, the only book you'll ever need. It's written so clearly that it's accessible to nearly anyone, but includes in-depth discussion of all the major brewing issues and techniques.
Principles of Brewing Science, 2nd edition by George Fix. A slim text, but packed with important information. Dense, but accessible to anyone with a scientific bent (no biochemistry background required).
New Brewing Lager Beer by Greg Noonan. Not just for lager brewers, this book reads like an expansion of Principles of Brewing Science, but benefits from the author's experience as a professional brewer. A must-read for anyone thinking of going pro.
Yeast by Chris White and Jamil Zainasheff. Very good discussion of yeast handling and fermentation practices. Some of the information is very much geared towards professional brewers with tens of thousands of dollars to spend, though.
For the Love of Hops by Stan Heironymous. Far and away the most readable of the science-y texts. More relevant information about hop chemistry, hop growing, and hopping techniques than you can find anywhere else.
Beer styles and recipe formulation:
Brew Like a Monk by Stan Heironymous. Very readable. This book is a great guide to brewing Trappist-style beer. (Also covers similar breweries like Duvel, Karmeliet, etc.)
Farmhouse Ales by Phil Markowski. An excellent guide to brewing saisons and bieres de garde.
Wild Brews by Jeff Sparrow. The only text available on sour and wild beers. Poorly written and short on information.
Radical Brewing by Randy Mosher. Probably the most fun brewing book I've read. A must-read for anyone who likes to experiment with new ingredients.
Designing Great Beers by Ray Daniels. Contains good information, but is quite dated, poorly organized, and not much fun to read. Still, if you want to brew traditional English- and German-style beers, it's worth reading.