I like Galileo's Middle Finger, by Alice Dreger. Her study of intersexed people brought her to what I think is one of the best ways of dealing with sex: defending those who would be harmed in the name of maintaining a strict two-valued approach. Here's a discussion. The book modified my view of the egregious J. Michael Bailey, publicizer of "autogynephilia," from Bad Guy to Asshole Who's Often on the Side of Good. She seems to attract those; the book has a blurb from Dan Savage.