The David Rumsey Map Collection has over 22,000 maps and images online. The collection focuses on rare 18th and 19th century North American and South American maps and other cartographic materials. Historic maps of the World, Europe, Asia, and Africa are also represented.
This is an incredible collection that contains something for everyone. In the video below, David Rumsey explains his interest in historical maps and how he has adapted them for use in GIS, online environments, and virutal worlds.