It's the most famous book by my favorite author, and I hadn't read it. It deserves its fame; it was good. There's two types of fiction; some books make you wish the world worked a certain way, some make you glad it doesn't. This is in the former category.
The Golem's Eye and Ptolemy's Gate by Jonathan Stroud
The second and final book in the series that began with The Amulet of Samarkand. For once, I'm happy to report that each book in the series got better.
I've recently read a bunch of other things, too, but I can't think of them right now...