Wow, I knew Words That Sell was good -- but is it that good? Does it really deserve to be named #1? Even I would have to argue that there are better books on the art of writing copy (John Caples' classic Tested Advertising Methods comes immediately to mind, despite the dull-as-dust title).
Words That Sell won't teach you how to write killer copy, though it includes some pithy pointers. It's the kind of book you keep on your desk for instant inspiration. It might be the most useful advertising reference book. But anyway, I'm delighted that the experts at About.com named it #1.