'Designing Great Beers' is worth checking out. It goes in heavy, gorey detail on several major styles, their origins, ingredients and style indiators.
Although it might get pooh-poohed by the purists, I got a great kick out of 'Sacred and Herbal Healing Beers: Secrets of Ancient Fermentation'. It has an enormous lexicon of herbs used in brewing in different parts of the wold throughout history, and a great exposition on mead. A must for anyone considering expeimenting with unhopped ale styles such as Gruit (go ahead - call me a heretic, I enjoy it). Last year I did some experimenting with an ale infused with rosemary. It got mixed reviews at a party but the general consensus was that it would probably go very well with chicken. Unfortunately, it never cleared completely so obviously some adjusting will need to be done if I don't try it again. The author of the book is a herbal-medicine type, so for each herb or adjunct there is an exposition of medical or psychoactive properties of the given herb. It's one of the favorite books on the shelf at my house.
'Brew Chem 101' is a good, accessible exposition of the basic chemical reactions that yeast perform to do their job. It goes over the chemistry that contributes to various wanted and not-so wanted flavors and describes conditions under which they occur.
'Brew Ware' is another essential for people interested in designing their own equipment on the cheap.