I know this is kind of degenerating into a discussion of DWJ, but she *did* write the book, and there wouldn't have been a movie without the book, so I guess it is okay. I'll be happy to discuss the movie more, but I feel like I already commented on it.
So I have been slowly making my way through all of Diana Wynne Jones's books. I started with Howl's and then read its sequel Castle in the Air, then made my way through the four Chrestomanci books, which I all highly recommend (Witch Week might have been my favorite, but you need to read The Lives of Christopher Chant and Charmed Life before you read Witch Week or Magicians of Caprona if certain characters are to mean anything to you). There is a new Chrestomanci book that I haven't read yet, so I can't recommend it. DWJ is very prolific--I've read Dogsbody, The Darklord of Derkholm, Witch's Business, Aunt Maria, Eight Days of Luke, Fire and Hemlock, The Time of the Ghost, The Ogre Downstairs, Mixed Magics, and The Tough Guide to Fantasyland (although the last is more of a spoof dictionary, not a novel).
I haven't read the Dalemark quartet or The Power of Three. If the latter is your favorite, stacer, I will definitely have to pick it up. I've also heard that Archer's Goon is the best, and I still want to read Homeward Bounders, A Tale of Time City, Year of the Griffin, Deep Secret, and the Merlin Conspiracy. And the new Chrestomanci book. She has so many good books!
I don't know if I could pick a favorite of DWJ. The one thing I can say of her is that I have yet to read a book of hers that I did NOT like--and considering the amount she has written, that is saying something.