Avid readers, what is the best book you've EVER read, the one you read again and again..?

I heard the Hunger Games series is great. My little sister is dyslexic so she hates reading, but she stayed up all night reading that series. I love the Hitchhiker's Guide to the Galaxy because its pure entertainment. It's hilarious! It has fantastic vocabulary too. I wish I had read it before I took the SAT's...