The University of Georgia's Rare Map Collection at the Hargrett Library, an outstanding collection of internet-accessible historical maps, including maps of the Western U.S. and the "frontier" period.
The University of Virginia Library's online exhibit, "Exploring the West from Monticello: A Perspective in Maps from Columbus to Lewis and Clark."
Travel the Highway of the Devil by four-wheel-drive vehicle.
The Illustrating Traveler
TIGER Mapping Service "Coast to Coast" Digital Map Database.
Maps of the United States
Aerial photographs of Several Regions
Map Machine from National Geographic
Geography - Welcome from The Mining Company
Earth Sciences & Map Library Home Page
Rare Map Collection
Bruce M. Gittings at the University of Edinburgh's index of WWW servers of GIS mapping sites.
The Center for Advanced Land Management Information Technologies (CALMIT) at the University of Nebraska-Lincoln provides lots of information on mapping technologies.