I have a couple of half-finished blogs, but I have to put them on hold to pay tribute to one of the great writers who has just passed away. If only I could come up with words to do her justice.
First I'll send you over to this post from Book Aunt, because she does a great job of summing up Diana Wynne Jones' multiplicity of books. Then you should read Jones' rather astonishing autobiography.
After reading about her life, it won't surprise you to hear that Diana Wynne Jones' books are odd, quirky, funny, "tilted away sideways*" from anything else you've ever read. Her writing is endlessly imaginative, sharply humourous, and deeply complex. There are books of hers I've reread several times and still don't get. My favourite books I reread often and get something new out of them every time. Even the lightest-hearted stories leave you feeling vaguely disquieted, as if some of your cherished assumptions have been subtly altered but you're not sure how.
Where should you start? You're most likely to be able to lay hands easily on Howl's Moving Castle and the Chrestomanci books, as they are justifiably her most popular works. The wizard Howl and Chrestomanci are both marvellous creations: powerful, arrogant, good but deeply flawed. And Sophie (of Howl's Moving Castle) is the best heroine ever. Period. Calcifer the demon is fasinating and the castle itself is brilliant; I could go on and on about Howl's Moving Castle. It's one of my all-time-favourite, bring-to-desert-island, reread-whenever-I'm-feeling-down books. The Chrestomanci books, besides having Chrestomanci himself (and don't we all wish there really were such a person, to step in and fix everything at the last minute, though not without challenging us to do most of the fixing ourselves, thus discovering our own hidden strength; and not without getting thoroughly exasperated at our ability to have screwed things up this badly in the first place) are a wonderful introduction to the Diana Wynne Jones' multiverse, her collection of parallel universes, most of which are far more interesting than our own. Here's a suggestion from her website about how to read the Chrestomanci books; like the multiverse itself, they proliferate in multiple directions, and it doesn't really matter which one you read first. They are short, easy reads and great fun, but there's a core of seriousness--Jones' villains are truly scary, once you find out who the villains really are.
My next favourite books after these (in fact, I may even like them more, but I don't have my own copies so I haven't reread them in a while) are The Dark Lord of Derkholm and Year of the Griffin. These are absolutely hilarious. They manage to be both a brilliant satire of the whole fantasy genre and perfectly plotted fantasy novels in their own right. I think I'm going to have to order these online because they should be in my library.
Then there are her books for older readers with seriously mind-bending concepts and narration: Hexwood and Fire and Hemlock are the ones I have read. If you like books where you're never sure what's real because someone is messing with reality, check these out. Dogsbody is another more serious novel for older readers, a wonderful, sad story that many people mention as a favourite (not nearly so mind-bending, in case you were worried).
She returns to the multiverse with The Merlin Conspiracy, which I could explain as Chrestomanci for people who can follow really convoluted plots--convoluted in a good way, with a crazy cast of characters and universes and an ending that comes much too soon despite the 472 pages. And she plays with reality again, doing yet another take on magical people who have to take care of things so everything doesn't fall apart, with Enchanted Glass. (Best use of vegetables in fiction, BTW.)
I'm going to go on a quest for Diana Wynne Jones books I haven't read yet (and she's a prolific author, so there are many). I'll let you know when I find more favourites. In the meantime, you can tell me which your favourites are. Let's make a point of introducing her to as many people as we can.
*A quotation from The Merlin Conspiracy