If you like The Subtle Knife by Philip Pullman
Here are some other titles you might enjoy reading.
Sabriel by Garth Nix.
This is a part of a trilogy. The 1st book is called Sabriel, and introduces us to the daughter of the necromancer Abhorsen, who must journey into the mysterious and magical Old Kingdom to rescue her father from the Land of the Dead. The 2 books that follow are Lirael and Abhorsen.
Stormbreaker - Anthony Horowitz.
This is the first in the Stormbreaker (Alex Rider) series. After the death of his uncle, who had been his guardian, fourteen-year-old Alex
Rider is coerced to continue his uncle's dangerous work for Britain's intelligence agency, MI6. The other books in the series are: Point
Blank, Skeleton Key, Eagle Strike, and Scorpia. Alex Rider: The Gadgets is being released in 2006.
Artemis Fowl by Eoin Colfer.
Twelve-year-old Artemis Fowl is the most ingenious criminal mastermind in history. With two trusty sidekicks in tow, he hatches a cunning plot to divest the fairyfolk of their pot of gold. Of course, he isn't foolish enough to believe in all that "gold at the end of the rainbow" nonsense. Rather, he knows that the only way to separate the little people from their stash is to kidnap one of them and wait for the ransom to arrive. This is also part of a trilogy.
Also by Philip Pullman is The Ruby in the Smoke. In 19th Century London, 16-year-old Sally, a recent orphan, becomes involved in a deadly search for a mysterious ruby.