Garth Nix is currently writing Clariel: The Lost Abhorsen, the much-awaited sequel to the Old Kingdom Trilogy (first book: Sabriel). He is currently estimating a 2013 release date.

I’m writing CLARIEL: THE LOST ABHORSEN at the moment. It is set about 300 years before the events of SABRIEL, in an extremely settled era of the Old Kingdom, where is almost no threat from the Dead or Free Magic, and the Abhorsens are considered something between an archaic remnant of worse times and municipal rat-catchers. Clariel will probably be a 2013 release.

The Old Kingdom Trilogy is set in a thrilling fantasy world featuring undead-creating necromancers fought by a mysterious figure known as the Abhorsen—whose duty is to undo their workings and enforce the magical Charter.