I just finished reading Mister Monday, the first book in Garth Nix's The Keys to the Kingdom series.
A great start to a promising series: "Seven days. Seven keys. Seven virtues. Seven sins. One mysterious house is the doorway to a very mysterious world -- where one boy is about to venture and unlock a number of fantastical secrets."
I'm definitely going to have to pick up the next two books Grim Tuesday and Drowned Wednesday since they are already out in paperback.