American Memory:  Map Collection:  1500-2003
Historic maps searchable by any term as well as topics such as cities/towns, conservation/environment, discovery/exploration, cultural landscapes, military battles/campaigns, and transportation/communications.  Also contains current maps from areas around the world (click on General Maps). http://lcweb2.loc.gov/ammem/gmdhtml/gmdhome.html

Perry-Casteneda Map Collection
Historical and current maps for all areas of the world.  Searchable by area.
http://www.lib.utexas.edu/Libs/PCL/Map_collection/Map_collection.html