The first book about the Zone diet, by Barry Sears. This was the first diet book I read and it blew my mind. I tried it out and quickly lost 20 pounds and felt much better (vastly improved concentration). I don’t follow the Zone as rigorously as I used to, but I still pretty much stick with it.
Sears has launched a website with additional information as well as food products with the 40-30-30 carbohydrate-protein-fat ratio recommended by the Zone diet.
In particular, the Zone Bars are pretty good, I think.