The 20 Best Marketing Books Of All Time (in alphabetical order):
The Anatomy Of Buzz by Emanuel Rosen. Before word of mouth marketing became a profession unto itself, Rosen was busy trying to figure out why certain brands get attention and how they do it. This is one of those classic business books that every marketer should read.
The Art Of The Pitch by Peter Coughter. If you are in marketing, you will have to get good at presenting and selling your ideas. I've read countless books on the topic, and this is the only one worthy of reading, studying and applying. Woe the marketer that doesn't heed these words.
The Cluetrain Manifesto by Chris Locke, Doc Searls, David Weinberger and Rick Levine. If you could point your finger at one book that changed the face of marketing, it would be this one.