My kids loved the Patricia Wrede Enchanted Forest Chronicals books (Dealing with Dragons, Searching for Dragons, etc.), and also anything by Tamora Pierce - she has a lot of strong female characters. My kids once gave up trick-or-treating (at the ages of 10 & 5) to go to a Tamora Pierce book signing on Halloween at a children's book store in our town -- that is how much they love her.