Compost: The Natural Way to Make Food for Your Garden by Kenneth Thompson
I've tried to read other compost books. They're either too vast, too detailed, too sciency, or too touchy feely. This book is the perfect balance. Kenneth provides all the science theory, details, and ratios - but also has a down to earth way of describing just what all that means and the bottom lines of what and what not to do.
I love this book - go out and grab a copy. And after that, go out and pee on your compost heap! (Read the book to find out why)