84: Revolution, by Jennifer Donnelly (2010 hardcover)

This is the second Donnelly book I read, and it was as good or better than the first. A troubled American teenager travels to Paris with her father and discovers a journal that takes her back centuries in time--in both a figurative and, eventually, literal sense. It's a great coming-of-age story combining history and fantasy in an engaging manner. There's lots to be learned here, and teen girls will love the romance and angst as well.