Behemoth by Scott Westerfeld

This book is an exciting middle entry in the Leviathan trilogy. The beastie of its title, the behemoth, is a bit of a deus ex machina that comes along at the end, but otherwise, it's a great story about two kids, who like each other despite being on opposite sides of World War I, who learn to trust each other and work together. It's done with a deft hand, and is a quite amusing read, even for adults. I'm looking forward to the final book in this trilogy, Goliath, which I believe will come out next year.