If you liked Artemis Fowl, you may like...

H.I.V.E.: the Higher Institute of Villainous Education (and its sequel) by Mark Walden.
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the Young James Bond series by Charlie Higston,
Chrestomanci series by Diana Wynne Jones
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Nightmare Academy by Dean Lorey
Grey Griffins series (1st title Revenge of the Shadow King) by Derek
Benz and J.S. Lewis
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Faerie Wars by Herbie Brennan
The Thief by Megan Whelan Turner
The Thief Lord by Cornelia Funke
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Keys to the Kingdom series Garth Nix
Pendragon series by D.J. MacHale
Underland Chronicles by Suzanne Collins
Alex Rider Adventures by Anthony Horowitz
Spy High series A.J. Butcher
Cherub series Robert Muchamore