I couldn't really think of a book that changed my mind or opened my eyes, but LOTR definitely impacted on my life by introducing me to fantasy [and subsequently sci-fi], gave me a real passion for the complexities of writing itself, and then with the movies turned into my first real fandom. I re-read it every year.

Life of Pi gets an honourable mention though, for being the book that came the closest to what I'd say was "opening my eyes" - just such an oh wow moment. Gorgeous novel, just beautifully told.