Out of the many books that I have read the one that is most influential to me would be Living Green by Greg Horn. I'm not sure that I can really count that, it wasn't really a novel. I learned many useful things from it and it convinced me to eat as organic as possible.
My most influential novels that I've read change all the time. Currently, for me, it is 'Simple As Snow.' I just finished reading it and it was an amazing read. The only thing is it is directed more towards young adults, which is what I am so I really liked it a lot.
also I just remembered another good one. This book is AMAZING I highly recommend it.
For One More Day - Mitch Albom