GeoSpatial One-Stop a catalog of geospatial information containing thousands of metadata records (information about the data) and links to live maps, features, and catalog services, downloadable data sets, images, clearinghouses, map files, and more.

• The National Map Seamless Data Distribution System  (USGS) provides data at the exact boundaries that you specify, information can be downloaded for free 100 MB at a time.

USGS GIS Map Studio is a collection of national and local services and data.

National Center for Education Statistics, the primary federal entity for collecting and analyzing data related to education.

Federal Geographic Data Committee

US Public Library Geographic Database includes the locations of America’s 16,000 public libraries, population characteristics from the US Census that best describe people that use libraries, and library use statistics from the National Center for Educational Statistics.

TerraServer - USA a collection of aerial photos, satellite images and USGS topo maps for download.

National States Geographic Information Council (NSGIC)

• GIS/Spatial Data Sets for Water
  

Mineral Resources On-Line Spatial Data

• National Hydrography Dataset
  

• GISDATA web mapping portal from the USGS: provides access to geospatial datasets that have been specially prepared for seamless access and delivery. NED, NHD, National Land Cover, nationalatlas.gov, Global Land Cover, and Global Topo GTOPO30.
  

ESRI Census TIGER 2000 data in shapefile format, users can choose multiple data layers for a single county or a single data layer for multiple counties and analyze them using GIS software.

 
ESRI - Downloadable datasets
ESRI World Basemap Data
GDT Dynamap/2000 U.S. Street Data
FEMA Q3 Flood Data
Census 2000 TIGER/Line Data
USGS NED Shaded Relief Imagery Data

Geography Network  an online resource to discover and access geographic content, including live maps and data, from many of the world's leading providers.

National Atlas of the United States

National Geophysical Data Center

National Park Service Geography and Mapping Technologies

National Wetlands Inventory Data

GIS Data Depot
- Digital Chart of the World (DCW) - E00 Format
- Administrative/Political
- Demographic Data
- Digital Terrain Elevation Data (DTED) Level 0
- Environmental/Natural Resource
- Geologic
- Hydrography
- NWI Wetlands - 24K - ARC/INFO Format
- Transportation
- USGS Quad Grids - Nationwide
- Wireless Telecommunications Data
- 7.5 Minute Digital Elevation Models