Back when I became a vegetarian, (waaay back!), I found a lot of articles by Victoria Moran (in Vegetarian Times, which used to be less of a recipe magazine than a magazine promoting vegetarianism more actively) really spoke to me. She seemed to be following the same path I was on at about the same time (so they didn't really influence me as much as reinforce what I was feeling).
Thrive is a recent book that has influenced some directional changes in my diet.
Other books are not as much influences (as in causing me to change in some way), but rather reinforce my beliefs:
The Diet Revolution (as well as Robbins' previous "Diet for a New America"), The China Study (T. Collin Campbell), Eat to Live (Fuhrman).
Going way back, I think one story (not a book) that influenced me (because I still remember it) was a short 1/2 column in a comic book!) that was a first person-story from the perspective of a puppy, who loved everyone and had many animal friends, and at the end, there was something about how he didn't understand hatred and not accepting others (other animals, in this case) because (last line).. "you see...I'm blind." Maybe corny, but my impressional pre=adolescent mind thought it was very touching and it brought tears to my eyes.