Altapedia
Geographical, statistical and sociological information on countries from A-Z, as well as full color physical and political maps of world regions. Altapedia also contains a "Resources" section that provides tools for teachers and students.
http://www.atlapedia.com/

Color Landform Atlas of the United States
Maps and links to information about each state. The site includes shaded relief maps, satellite images, 1895 maps from the Rand McNally Atlas of the World, topographic maps, and county maps.
http://fermi.jhuapl.edu/states/

How Far Is It?
Calculate the distance between two locations ("as the crow flies").  Hosted by Indo.com, this site uses the longitude and latitude of cities around the world to calculate the distance between them. A map showing both places is also provided.
http://www.indo.com/distance/

Mapquest
One of the most popular mapping sites on the Internet, Mapquest provides maps, driving directions with estimated times and information about destinations.
http://www.mapquest.com

Map Collections 1500-1999
Historical maps from the Library of Congress' American Memory Project. This fully searchable collection is divided into seven categories: Cities and Towns; Conservation and Environment; Discovery and Exploration; Cultural Landscapes; Military Battles and Campaigns; Transportation and Communication; and General Maps.
http://memory.loc.gov/ammem/gmdhtml/gmdhome.html