Freakonomics, by Steven D. Levitt and Stephen J. Dubner
Possibly the most interesting social science book that I've read. Levitt is a brilliant applied microeconomist who exposes cheating by schoolteachers and sumo wrestlers, looks at the franchise-style organzation of street gangs and explains why crack dealers still live with their moms, links the drop in crime of the 1990s to Roe v. Wade and the legalization of abortion, and analyzes issues regarding parenting.
If you're a social science nerd, go buy/borrow/steal this book -- right fucking now.