Worldview Neuralgia (don't call your customers liars)
If I had to pick a book of mine to recommend that you haven't read yet, it would probably be All Marketers are Liars.
The reason you haven't read it, I'm guessing, is that it has a terrible title and had a worse cover. Lesson learned. All the details are right here on this little sub-blog.
[Two other book updates: Purple Cow now comes with a new appendix, written by you, my readers. The rest of the book remains the same. And the best of the last three years of this blog are now collected in the Kindle-only book called Zen Unicorn.]