Patricia C. Wrede is one of my all time favorite writers. This is the first book I read by her when I was young and it got my hooked. I think the rest of her books are even better than her dragon series. Try Mairelon the Magician or the Lyra novels.
My father read this to me as a child, and inspired my love for fantasy, science fiction, and (with a little poetic license) computer science. Great for kids, adults, and people looking for another page-turner after Harry Potter.