It may sound a bit silly, but my favorite book of all time is The Last Unicorn. by Peter S. Beagle. It seems like such a simple story, but woven into it are so many profound statements about life and mortality. I read it over and over again, and it seems to grow more and more beautiful and meaningful each time I read it. I've read a great number of the classic books written throughout history, and I have yet to find anything that emotionally moves me so much as this reasonably short, sweet, lovely book.
I also absolutely love Watership Down, Ender's Game, The Power of One (every chicken lover should read this book--the main character's best friend growing up is a rooster named Granpa Chook! Just a fantastic book in general, too), Beloved, Fluke, The Poisonwood Bible, and One Flew Over the Cuckoo's Nest. Much like my music tastes, I don't like to stick to just one genre, subject matter, or type of book--I'll read pretty much anything that looks "interesting" no matter what it's about.
As far as non-fiction books go, I really liked Thanking the Monkey and Old Souls. Probably others as well that I can't remember off the top of my head.