1. The Inheritance Series by Christopher Paolini
2. Harry Potter Series by J. K. Rowling
3. The Sea of Trolls series by Nancy Farmer
4. The Dresden Files by Jim Butcher
5. The Lord of the Rings by J.R.R. Tolkien
6. Percy Jackson and the Olympians by Rick Riordan
7. Hitchhikers Guide to the Galaxy by Douglas Adams
8. A Song of Ice and Fire series by George R.R. Martin
9. Insomnia by Stephen King
10. The Dark Tower series by Stephen King
Honorable mentions:
The Talisman and Black House by Stephen King and Peter Straub. This would have made the top ten if I wasn't so indecisive.
Artemis Fowl series by Eoin Colfer. That was my childhood.