Many cookbooks have changed my life! NT did way back. The Garden of Eating is a great one too. I adore Full Moon Feast-I love how she views traditions in food. But the ones that changed my life the most in terms of how I eat and my health were the Raw Gourmet and Living on Live Food.
Four years ago I got the Raw Gourmet and was fascinated...but not ready to implement what I learned. Slowly the knwledge crept in and I incorporated dishes here and there. LOLF made it a snap to be 90+ raw. I'm not looking to be 100% but I love that this book made my kids beg for raw veggies and is free of most of the common allergens.
Its not a recipe book. Its a COOK Book. And it teaches you the absolute fundamentals of cooking and preparing anything in the world, so you basically don't even need recipes anymore. It does have a lot of sample recipes, esp for the basics (i.e. sauces, broths, etc).
Cook's Illustrated New Best Recipes for technique.
Nourishing Traditions for a whole new perspective on food (though I haven't made many of the recipes yet).
Animal, Vegetable, Miracle for beautiful prose and more good perspective on food sources.
My favorite Moosewood book (I have several!) is Sundays at Moosewood. I've also used the original Moosewood and Enchanted Broccoli Forest quite a bit. I like Moosewood Kitchen Garden books too. yeah, they are all pretty good! I was veg for over a decade and these helped me learn to cook that way.
Martha Stewart is pretty reliably good too (I like my huge appetizer book and Healthy Quick Cook- the first book I had that divided things seasonally!).
I can't wait to get Full Moon Feast. I've been wanting it for months!
All of these had a big impact on my at the time in my life that I discovered them and continue to be favorites!