Mount Vernon to overlay onto Google Earth imagery. (I'm publishing a video about that later this week). I was able to find exactly what I was looking for in the historical map collection available through the Library of Congress. LOC's online historical map collection has nearly 38,000 items for visitors to view. Many of the maps are in the public domain or have Creative Commons licenses. You can browse and search for maps in the collection according to date, location, subject, language, collection, and contributor.
Applications for Education
Historical maps can provide students with perspective on how physical and political landscapes have changed over time. Putting historical and current maps side-by-side is one of the easiest ways for students to see and make comparisons. Layering historical maps on top of current maps is another good way to do that. Google Earth makes layering maps possible.