I have to recommend my favorite, it's not a diet book per se, but it is the book that put me on the path to permanent weight loss.
Super Foods Rx: 14 Foods that Will Change Your Life - this book really made the science of nutrition accessible to me.
All 4 of my grandparents died relatively young - diabetes, cancer, heart disease and complications of heart disease. I decided to start eating FOR long term health. Spinach for my eyes, blueberries for my brain, tomatoes to help prevent cancer, nuts to help prevent heart disease.
It made a huge difference in my weight loss. I made goals of the number of different super foods I would eat every day. When you're trying to eat blueberries and oatmeal and sweet potatoes and salmon and yogurt and walnuts and oranges and spinach in one day (for example), there just isn't much room for unhealthy stuff!
Definitely definitely an inspiring book for me.