Digitized Atlas from the Perry-Castaneda Library

The Perry-Castañeda Library Map Collection at the University of Texas at Austin (an essential site for map and geographic research) has digitized the full text and images of eight historic atlases and made them available online.

+ Army Map Service Topographic Map Series (1945-)
+ Atlas of Mexico (1975)
+ Atlas of Texas (1976)
+ Cambridge Modern History Atlas (1912)
+ Historical Atlas by William Shepherd (1911)
+ Historical Atlas by William Shepherd (1923-26)
+ National Atlas of The United States of America (1970)
+ Public Schools Historical Atlas by C. Colbeck (1905)

(Source: ResourceShelf)

Census Tract Shape Files

and data from the 1940 census onward are downloadable from the National Historical Geographic Information System (NHGIS) web site. It's a cool site. Also explore Social Explore Site for interactive maps with historical census data.

NEW: NASA's World Wind Digital Globe-3D Cross Section Viewer

is just released. "This plug-in allows you to select a square area of terrain and view the ‘cut-out’ in a separate 3D window - the terrain viewer."
http://www.worldwindcentral.com/wiki/ 3D_Cross_Section_plugin_and_viewer
(Source: ResourceShelf).