Re: what non-fiction books have you read? please rate it ...
The Golden Ratio. It's all about phi, the most important irrational number. A great deal of time and effort is spent debunking: a) various ancient societies' understanding and/or application of the golden ratio; the alleged aesthetic perfection of the golden ratio; c) various artists' applications of the golden ratio within their works; c) etc., etc., ad infinitum, ad nauseum. The math is fascinating. The explanations of the natural occurences of phi are mind boggling. The proofs are accessible to someone who understands and enjoys mathematics but not calculus (me).
I would heartily recommend it to anyone who is not afraid of a little algebra, a little history, a little philosophy, and a little critical thinking. It does get a little long winded, especially for such a short book, and has made it's way into my car, where I read it while I wait for whatever I might be waiting for.