A new book I highly recommend is 'Sustainable Energy - Without the Hot Air' by David MacKay, a physicist at Cambridge University. You can download it for free or buy a hardcopy. Reviews from The Economist and Boing Boing echo my feelings. MacKay's book is entertaining, insightful. witty, accessible, educational and no nonsense.
In his book, MacKay mentions a book by another physicist, Caltech professor David Goodstein's 'Out of Gas', which I also recommend.