Well it goes without saying that the best book anyone will ever read is 'The Book' - a literal translation of The Bible's title.
But after that, like someone had said before, Orwell's 1984.
I did read the shit out of some Dean Koontz for a while. It seems to me people who like Koontz like Stephen King, people who like Stephen King like Dean Koontz, but really I have read a few Stephen King books, and I do not care to read more. Nothing against him, it's obvious he's a good writer, I just don't like his style. Dean Koontz I feel captures the insane brain and the thoughts the people must go through in his books a lot better. Also his raw violence and intense action scenes are well enough captured if you have even a tiny imagination to picture them.
Of course, I went through a goosebumps kick as a child, and I read the hardy boys in my early teen years, and I was the only one ever, I can imagine, to like the boxcar children, which was in between the last two.