The TIGER/line files

The U.S. Geological Survey's TIGER/line files constitute a digital base map of the entire United States. These files include spatial data for such geographic features as roads, railroads, waterways, and political and census boundaries (e.g., boundaries of tracts and block groups).

The Tiger/line files are available in several editions. The University of Chicago Library and most other depository libraries have copies of each of these editions; you may copy them freely.

The TIGER/line files themselves cannot, unfortunately, be used by most commercial mapping programs. You need to convert them into the appropriate format. You can also download certain editions of these files from various sites.  For example, ESRI will let you download a nearly complete version of Tiger-based shapefiles for the 2000 census.