Empire of Ivory (Naomi Novik, 2007) is the fourth book in Novik's series about an alternate world in which the combatants in the Napoleonic Wars have air forces of dragons and their aviators as well as armies and navies. While I don't think it's quite as brilliant as the first book, His Majesty's Dragon, IMHO it's stronger than books #2 and #3, with a tighter plot arc and a strong hook at the end to make the wait till 2008 for the next volume seem endless.
I promised friends who haven't read it yet that I wouldn't spoil it, so there's not a whole lot more I can say, except that I like how Novik is expanding her world and focusing more on the differences dragons make in the intercontinental balance of power in the 19th century. Which sounds dry as dust, but this is a page-turner. I started it at 7:00 last night, pausing only to play with my daughter and watch The Office, finally going to bed at 12:45 a.m. with ~30 pages to go, which I finished on the bus this morning.