Doug Abrams

80% of this book is all about why you should, y'know, communicate with your baby, instead of ignoring them. Then there's a glossary of signs that will be really useful to you and your child (diaper, eat, sleep) and others that seem so very not-useful, but most of the pictures demonstrating all the signs are small and hard to understand.
Better source: http://www.signingsavvy.com/ for a video dictionary.