Google Maps provides maps and satellite photos for most of the United States and some international locations.
Knowledgeplex provides information for those interested in affordable housing and community development. The DataPlace section provides demographic data on U.S. Communities.
Terraserver, run by the U.S. Geologic Survey, provides detailed aerial photographs of much of the United States.
The Census website provides detailed demographic information from the 2000 Census, GIS information and estimates of demographic information in the years since the 2000 Census.