What are the books that permanently and profoundly altered your way of looking at life or how you perceive reality? I respectfully suggest that we not include the Bible, the Quran, The Book of Mormon or any work that forms the basic text of a particular religion since these answers would be more indicative of a person's religious persuasion than how his or her life has been affected by engagement with the world of books and ideas.
For me, these two choices come immediately to mind:
Pedagogy of the Oppressed by Paulo Freiere
The Nature and Destiny of Man (volumes I and II) by Reinhold Niebuhr