Word Origins -- And How We Know Them : Etymology for Everyone, by Anatoly Liberman

Well, not everyone. "Everyone" with a pretty high level of interest in the subject, and above-average intelligence. Liberman is very quick-witted and assumes a basic working knowledge of etymology, which I admit I don't have. On the other hand, towards the end, he mentions that he hopes that his book might be considered as a basic textbook, and for that it would work VERY well--best textbook I think I've ever read start-to-finish. While fairly short, this is a good overview of theory and practice, but if you don't know anything about the Great Vowel Shift in the English language, I'd steer clear.