I've got three kids aged between 10 and 15, and by checking out the horribly damaged sections of the bookcases - these are the best authors:

Jacqueline Wilson
Terry Pratchett
Christopher Paolini
Lemony Snicket
Philip Pullman
Eoin Colfer
J.K. Rowling
Louise Rennison
C.S. Lewis
Garth Nix
Roald Dahl
Andre Norton
Anne McCaffrey

I can't rate the newer books, but I grew up on a steady diet of C.S. Lewis and Andre Norton.