These are free, historical atlases and maps of the US and each individual state. “Historical maps can be an exceptional tool when you are beginning a genealogy research project. Because maps can give you important details about business and property ownership, they can be a significant source of information. This information can tell you what and whom you need to research to learn more. The goal of this site is to help you discover important information to get started.”
These maps include all county boundary changes in rotating animation. “Past and present maps of US are overlaid so that you can see the changes in boundaries, downloadable County DOT Maps, and state atlas maps.”
This site also has some military battle maps and will be adding more. Current military maps include maps of the Revolutionary War and Civil War campaigns.