Christopher Paolini is #1! I got Inheritance the day it came out and it is the best book EVER!
2: JRR Tolkien (Lord of the Rings is awesome, plus my favorite movie!)
3: John Flanagan (Ranger's Apprentice, great series in general. Isn't there a new series by him, The Brotherband Chronicles?)
4: JK Rowling (Harry Potter is just a great series, and Deathly Hallows is the best)
5: Rick Riordan (Greek mythology in the real world? What's not cool about that?)
I love loads of other series, but these are my favorites. Some honorable mentions are Suzanne Collins and Anthony Horowitz.