Since any serious player knows that a poker strategy book is pretty much worthless, Elements of Poker talks about stuff besides ZOMG, raise when you have AA UTG. Tommy Angelo is a world renowned mental game coach for Krantz, Raptor, OMGClayAiken etc. The book talks about how to be a better poker player, but not in a strategical sense. It has a few different topics, but by far the part that made it worth the money to me was the stuff on quitting. Quitting when you are winning, quitting when you are losing, quitting when you are bored, etc. He talks about the factors you should be looking for to know when you should quit a game.
I was already a winning 400NL player making 10-15k+ a month when I bought this book and it easily improved my game.
Elements of Poker - That is a non-affiliate link
Here is a list of articles from his site - some of these are in his book
http://www.tommyangelo.com/articles.html
I highly recommend reading "
Reciprocality: The Cause of Profit at Poker" from his articles.