Jenny's Books has declared the week of August 1 through August 7 to be Diana Wynne Jones week and invites everyone to read along with her. I think it is a great idea. I suggest going to the library and grabbing any of her books they have on the shelves, but if you're feeling like being selective, aim for Eight Days of Luke, Fire and Hemlock, Howl's Moving Castle, Archer's Goon, and Enchanted Glass. That ought to be enough to get you started.
On a more sober note, now might be a good time to write to Diana Wynne Jones and let her know how much you've enjoyed her books. She's struggling with breast cancer. There's an email address given here, or you can write to her at:
Diana Wynne Jones
c/o Greenwillow Books
10 E. 53rd St.
New York, NY 10022
The official website adds "no questions, please." So--take a minute to write, even a short note (I've seen a couple of really great letters reproduced on blogs. Mine was just a quick "Thanks! I love your work." Somehow, I always end up really tongue-tied when I most want to praise).