Just finished reading Every Soul a Star by Wendy Mass - recommended by my 9 year old daughter. Great reading for 9-12 year olds - particularly girls, though it's not a really "girly" book...and good reading for their parents as well.
If your kids enjoyed Harry Potter, thet might also like: Children of the Red Kings series by Jenny Nimmo So You Want to Be a Wizard series by Diane Duane
Also check out: The Sisters Grimm by Michael Buckley and Peter Ferguson The Mysterious Benedict Society by Trenton Lee Stewart and Carson Ellis His Dark Materials series by Phillip Pullman (Don't be discouraged by that abyssmal Golden Compass movie. The books are terrific.)