I rarely every recommend books here, as you know I normally stick with forum coverage and conferences. I finally finished reading John Battelle's book, The Search, and I would feel guilty if i would not recommend to you guys to buy a copy and read it yourself.
I have never felt so strongly towards a book in this industry before. Let me tell you, this book is not about how to rank well in Google (you already know that). It is about how Google got itself to rank so well in the industry. This book, will however, make you as an SEM/SEO think about the future of search in ways you have never imagined.
It is worth the money, it may even change your life.
For more information on the book, visit http://www.battellemedia.com/thesearch/.
P.S. John has no idea I wrote this, he didn't even know that I was reading it.