The Encyclopedia of the English Language: well done and interesting, with sections on the history, grammar, vocabulary, use, and variation of the language. Each section has lots of examples and pictures, including original source material dating back to Saxon times. The book is written from a British point of view but does a good job of discussing other forms of English without value judgments -- in fact, the varying regional standards are one of the main subjects of discussion. One caveat: this will be pretty technical for someone without at least a little background in linguistics. The author explains most of his technical terms, but makes extensive use of the International Phonetic Alphabet to describe pronunciation -- and this is NOT the phonics you learned in grade school. (On the other hand, how else could you do it?)
Generations: A Century of Women Speak About their Lives: An extremely interesting book, describing the lives of 3 generations of women in their own words. The thing that fascinated me most was the wide variations of mores and behaviors even among women of the same generation (especially notable in the oldest women) in such areas as dating, premarital sex, work inside or outside the home, and relationships with spouses. This book proves the impossibility of generalizing about 'The Old Days'.