Rent 1632 (Assiti Shards)

This book was recommended to me by a middle school student of mine, so I wasn't exactly expecting total brilliance. I'm going to find that child tomorrow and thank him for telling me about it. This is a wonderful alternate history, up there with Harry Turtledove for me. It is well written with good characters and the action is great. I think my favorite part is that the Americans in the past don't just slid into the ancient world like a lot of time travellers do, they actively take a role in making a better world. And they don't do it for their own gain, but to eliminate some of the worst of modern history Nazis. Highly recommended.