USGS Historical Map Explorer
Search using a graphical map interface for all historic topographic maps that covered selected location; free download of scanned maps
TopoView
Search using map interface, by place name or quadrangle name; includes all topographic maps from 1884 to the present with free download in multiple formats
USGS Store Map Locator
Another way to look for USGS topographic maps; download options not as flexible as TopoView
Historical Maps Online
UIUC Library scanned map collection includes earliest edition of many 1:62,500-scale Illinois topographic maps
1:250,000-scale US Topographic Maps
Available from University of Texas at Austin; JPGs of multiple editions
Digital topographic mapping created by most nations is available only by purchase. Some US-produced topographic maps for other nations has been scanned and is available freely online.
US-Produced Topographic Maps for Other Nations
Available from University of Texas at Austin; JPGs of sheets from different US federal agency sets, organized geographically and alphabetically
Germany Topographische Karte 1:25,000
Available from Brigham Young University. Includes links to Internet Archives scan of gazetteer volumes. Search by sheet number; zoom, pan, and download.