July's recommendation: Howl's Moving Castle, by Diana Wynne Jones.
It's a good thing no English teacher ever asked me to analyze John Donne's poem "Song;" my answer would have appalled them. "It's a curse, y'see, that the Witch of the Waste placed on Howl, and when all the terms of the poem are fulfilled . . . ." Howl is a wizard, and he lives in a moving castle, as you might guess from the title. The castle wanders around the hills above the town of Market Chipping, belching black smoke out its turrets and terrorizing the inhabitants. But Sophie -- who is the eldest of three sisters, which is of course terribly unlucky; "everyone knows you are the one who will fail first, and worst, if the three of you set out to seek your fortunes" -- gets inside the castle, and finds out that things there are even odder than you might expect from the exterior (and a migratory castle isn't exactly normal).
There's Howl, all right, a self-centered man who spends hours in the bathroom every day making himself pretty; Michael, his harried apprentice, who may or may not actually be learning anything from Howl's "lessons" (when he remembers to give any); Calcifer, the whiny, stubborn fire demon who's somehow bound to Howl (or is Howl bound to him?); and assorted odd visitors like a dog who keeps turning into a man and then a different kind of dog, an animated scarecrow that refuses to go away permanently, and of course Sophie herself, who in the space of about a day goes from interloper to permanent fixture who's determined to clean the whole castle, top to bottom (it's filthy).
Sophie's under a spell; Howl's under a curse; Howl and Calcifer are bound together by some sort of contract; and then there's the real threat, the Witch of the Waste. Howl may be dishonest and amoral and a terrible flirt, but he's not evil the way the Witch is. At this point I'm looking back over this description and realizing that it's one of the more disjointed things I've ever written, but it's hard to step back and view this book from a distance. It's funny and has some great turns of phrase and some really interesting touches, like the fact that the castle door, from the inside, opens on four different places -- the hills above Market Chipping are only one of them -- and then there's the poem, tying it all together, from several directions at once (very literally). Sophie needs Calcifer's help to get the spell off her, Calcifer won't help her unless she breaks the contract between him and Howl, and then the curse steps in and makes everything more complicated, in a very wonderful way.
There's a sequel of sorts to this book, Castle in the Air, which I don't love quite as dearly, but which is fun nevertheless. For starters, you can get a great deal of entertainment out of trying to figure out how the hell it's a sequel, since it starts in another country and does not appear, for the longest time, to have anything to do with the characters of this book. And I'd have to say that the worst book I've ever read by Diana Wynne Jones has more of fun and whimsy that carries unexpected substance than the best books written by a lot of other children's/YA authors out there. Oh, yeah, did I mention this is a kid's book? But like J. K. Rowling, Diana Wynne Jones is an author you can enjoy at any age. I took all of her books with me to college, and I still read them now. You should, too. :-)