Contains various map databases on topics including topography, biodiversity, water use, etc. Also contains links to other GIS data sources. A good starting point for searching for GIS data from the United States.
This geographic names data set provides a "mashup" of URLs for official city and county government web sites and city and county location data from the USGS Geographic Names Information System (GNIS). GNIS data includes incorporated places, census designated areas, unincorporated places, counties, and populated places.
The U.S. Census Grids provide raster data sets that include not only population and housing counts, but a wide variety of socioeconomic characteristics. These gridded data sets transform irregularly shaped census block and block group boundaries into a regular surface – a raster grid – for faster and easier analysis.
S. Ahern, M. Naaman, R. Nair, and J. Yang. JCDL '07: Proceedings of the 7th ACM/IEEE-CS joint conference on Digital libraries, page 1-10. New York, NY, USA, ACM, (2007)
J. Owens, M. Yuan, M. Wachowicz, V. Kantabutra, E. Jr., D. Ames, and A. Gangemi. National Endowment for the Humanities Workshop Visualizing the Past: Tools and Techniques for Understanding Historical Processes, University of Richmond, Virginia, USA, volume 188 of Frontiers in Artificial Intelligence and Applications, IOS Press, (2009)
L. Stenneth, O. Wolfson, P. Yu, and B. Xu. Proceedings of the 19th ACM SIGSPATIAL International Conference on Advances in Geographic Information Systems, page 54--63. New York, NY, USA, ACM, (2011)
E. Valle, H. Qasim, and I. Celino. Proceedings of 1st International Workshop on Pervasive Web Mapping, Geoprocessing and Services (WebMGS 2010), (2010)