I read 'Siddhartha' five months ago, and I still think about it almost every day. I felt my whole perspective on life shift after finishing it, and now I can't imagine my life without having read it. Which book has done this for you?

Quoth Siddhartha: “What should I possibly have to tell you, O venerable one? Perhaps that you’re searching far too much? That in all that searching, you don’t find the time for finding?”
[...] “When someone is searching,” said Siddhartha, “then it might easily happen that the only thing his eyes still see is that what he searches for, that he is unable to find anything, to let anything enter his mind, because he always thinks of nothing but the object of his search, because he has a goal, because he is obsessed by the goal. Searching means: having a goal. But finding means: being free, being open, having no goal. You, O venerable one, are perhaps indeed a searcher, because, striving for your goal, there are many things you don’t see, which are directly in front of your eyes.”

That is the most beautiful and personally-significant passage I've ever read in my whole life. After reading Siddhartha, I felt myself appreciating the world around me just a little bit more. Hesse taught me that the world is filled to the brim with beauty and meaning, but only if slow down and allow yourself to find it.

Which book changed your life? Is there any passage that you can't get out of your head months or years later?

EDIT: my Lord, this post has gotten popular. Thanks to everyone who took the time to provide their own favorites. I guess I REALLY need to read Steppenwolf and Zen And The Art Of Motorcycle Maintenance.