Flim-Flam by James "The Amazing" Randi; 1998, Prometheus Books
One thing you can say about James Randi is that he puts his money where his mouth is. He makes this abundantly clear throughout this book, which includes several accounts of people who tried to claim his renowned $10,000 (now up to $1 million, still no takers) prize for an authenticated paranormal phenomenon performed under rigorous laboratory conditions. This offer, which some have slurred as a "stunt", is actually typical of Randi's extremely practical, common sense, hands-on approach to debunking.
Unlike most of those who share my bibliography with him, Randi is not a trained professional scientist. Rather, he makes his living as a stage magician. His skills are a valuable complement to those of the scientists; they usually know when there is a theoretical reason to distrust a claim, but Randi knows when there is a physical reason - whether it's a spiritualist tipping tables, a psychic performing a cold read, or a dowser unconsciously causing his own rod to twitch, Randi usually knows how it (or something similar) can be accomplished with no help from the supernatural. And lo and behold, in every case so far, that turns out to be how it is, in fact, accomplished. Because of this focus, Randi deals with a slightly different subset of material than the other books on my list; he mentions Creationism only once, for instance, but devotes entire chapters to spoon-benders and water witches. Though some claim that it is a waste of time to debunk such small fry, Randi points out numerous instances where petty chicanery or delusion have cost innocent bystanders time, money, or even their lives.
It is often said that Randi is an asshole, and in fact he records a couple of instances where people seem to be made genuinely miserable by having their delusions snatched. To which I say, so what? The truth is the truth whether you're particularly happy about it or not. Randi assists in seeking out the truth, going up against those who are actively trying to obscure it. He also writes entertainingly and bluntly about his experiences. By all means, read this book.