What book(s) did you read that made you really sit back and think about what they were saying. Or even, have shaped some of your values or beliefs. (The bible for some would be an obvious answer ;p)
This could have been read at any point in your life. Was it a Dr. Seuss book about eggs and ham? Possibly something they forced you to read in high school? Whatever, if it made you think I want to know!
For me, Ishmael by Daniel Quinn made a definite impact on my morale fiber. It gave me some solid answers to my questions about how this shit storm came to be, and how we may be able to correct it all. An interesting read for anyone out there that is, even the slightest bit, concerned about the world.
Lolita. I've not finished reading it yet, but... it's grounded me. I'm no longer lost in some stupid idealistic world that all paedophiles are wonderful beings with the child's best interests at heart, and that all the abusers are mothers and mere situational heterophiles. Which obviously has "reset" my moral code somewhat.
Ulysses
Iliad (epic poetry)
Odyssey (epic poetry)
Seven Pillars of Wisdom (which I have 1st edition ;) )
Ivanhoe
And above all else, the Harry Potter series.