His Dark Materials Triology by Philip Pullman

This trilogy follows the adventures of a young girl named Lyra, her daemon familiar, and, in the second and third books, Will. Lyra lives in a world where bears wear armor, a person without a daemon in an outcast zombie, and creatures rip out people's lungs. Will lives in a world very much like ours. Lyra and her daemon, Pantalaimon, meet Will in a rather violent way in the second book, The Subtle Knife. In the book, Will and Lyra meet by striking blows at each other then finding that they become the best of friends. The three of them venture into another world full of ghostlike creatures called Specters. The world they ventured into hosts a knife of unspeakable power. The knife was a weapon that could cut through any substance. In the final book, The Amber Spyglass, the children must find a way to stop an important substance called Dust from falling into an abyss. How will they stop the Specters and the abyss from sucking up all of the dust?
I liked these books because they were fast-paced, full of action, and had many interesting creatures.
-- Kevin N.