Many maps produced by the U.S. government (including topographical maps) may be viewed and ordered online:
An excellent website for international maps:
Hemispheric, country, island, province, state and territory maps, current time and date, bodies of water, country and state flags. Map tests and answers.
David Rumsey Map Collection Cartography of the Americas form the 18th and 19th centuries.
Historical Map Collection Perry Castenada Library, University of Texas - Austin
Rare Map Collection at the Hargrett Library University of Georgia.
Wisconsin Historical Society Browse or search for Wisconsin historical maps