http://www.animatedatlas.com/movie.html
This is an animated atlas that displays the geographic history of the United States of America, beginning in 1789. It is really unique in that it is animated and, therefore, is a single map that changes as you progress along the time line at the bottom. The atlas discusses changes due to wars and relations with other countries, growth and expansion over time, and battles within the US. You have the option to either play straight through or break it up into three sections of history, completion of territory, the civil war, and post civil war.