Found this gem of a book while browsing del.icio.us/popular/. I not sure if compsci books are getting easier to read or if I'm just getting better at reading them. Either way, this one looks fantastic.
N.B. I used to think that making books free for download would reduce the income you'd get from them, but since then I've bought a number of books that I wouldn't have done if I hadn't been able to browse them online first. (the last one was Practical Common Lisp, which is thoroughly excellent btw)