The Outsider by Albert Camus. Good to read when you're a teenager.
The Castle by Franz Kafka. I think most people prefer The Trial, but The Castle is more cyclical, even more damning on our ability to reach something (god/ salvation?)
Long Walk to Freedom by Nelson Mandela. Humbling.
The Autobiography of Malcolm X by Malcolm X and Alex Haley. See above. Just when he had alighted on the correct path.
Winnie-the-Pooh by A.A. Milne. I only read this for the first time a few years back. Really funny, and touching. The ending of the second book is somehow incredibly sad.
American Psycho by Bret Easton Ellis. Not much I can say about it. Black comedy doesn't really come close. And to have a whole chapter about Phil Collins...
Spring Snow by Yukio Mishima. I love Mishima's work, but I'm not sure I ever fully understood the tetralogy of which this book is the first part. It works as a standalone book.
Catch-22 by Joseph Heller. My favourite book. Absurd, but realistic in the extreme. I laughed a lot.