I love
Isa Mascowitz. Her website was pretty essential to me when I first became vegetarian.
The first book that made me think about becoming vegetarian was the book
Healthy at 100 by John Robbins (of Baskin Robbins fame). I found it comparable to the China Study. In fact, the China Study is mentioned a lot in the book.
I also remember that
Love Yourself Thin by Victoria Moran really impacted me when I was a freshman in college. I cannot recommend this book highly enough to vegetarians with disordered eating/emotional eating issues. Fantastic.
For someone who is just starting out or is just dabbling in vegetarianism, I would recommend
How to Eat Like a Vegetarian. It has some great transitioning ideas. Very simple and easy. Nothing is too complicated.
Vegan on the Cheap is great! So many tips and tricks and substitutions. Very easy and cheap food (but not cheap as in crap). Perfect for a beginner.
Finally,
The Great Vegan Bean Book has some very interesting ideas. Bean cookies? I admit that I have not tested this book, but definitely some interesting stuff in it.