Information about web sites that host large amounts of GIS datasets both at the nationwide (United States) and global levels. Most of the GIS data is available for free or for little cost.
EROS Data Center
The USGS EROS Data Center houses millions of aerial photographs of the United States, as well as images from several series of satellites covering the entire Earth.
Federal Communications Commission Datasets
Mostly MapInfo format vector datasets available for free download. Data examples include census data, FM Broadcast zones, and Guam mapping areas.
Commercial data service. You can access free USGS DRGs.
National Atlas of the United States has nationwide datasets to view and download as ArcView shapefiles.
United States GIS Data Repository
The USGDR is a new data source that operates on the principle of “Making Public Data Public”: that if taxpayer dollars are used to create data, and that data is not critical to national security, then it should be easily available to the public. The USGDR runs entirely off sponsors and donations.
USGS Geographic Data Download
Access to a wide variety of public domain data from USGS at a variety of scales. This page also contains information about converting SDTS and other formats to GIS compatible types.