Beyond Freedom and Dignity by B.F. Skinner is probably the best nonfiction book I've ever read. It not only contains profound philosophical insights, but presents them in a concise and approachable manner. Every chapter ends with a recapitulation of the chapter's contents (why isn't this standard?). The book is short and deals with a single topic. It gets to the point rather than beating around the bush, and completely avoids invoking metaphysical explanations or political implications. I truly cannot praise it enough.