<URL:http://www.usgs.gov/data/index.html>
  U.S. Geological Survey (USGS) data products, including cartographic data, geologic data, water data, and links to other USGS machines which hold data or metadata archives.

<URL:http://sun1.cr.usgs.gov/eros-home.html>
  U.S. Geological Survey's EROS Data Center (EDC).  Aerial photography, 
cartographic data, earth science data, hydrologic data, landuse/landcover data, radar data, satellite and satellite derivative data, topographic data.

<URL:http://sun1.cr.usgs.gov/landdaac/landdaac.html>
  Earth Resources Observation Systems (EROS) Data Center Distributed Active Archive Center (EDC.DAAC).  Archives include land processes data, including satellite- and aircraft-acquired data:  1km AVHRR, Landsat Pathfinder data,
Digital Chart of the World Derived Digital Elevation Model Data (topographical charts), SIR-C/X-SAR (Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar). 

<URL:http://www.ngdc.noaa.gov>
<URL:gopher://gopher.ngdc.noaa.gov>
<URL:ftp://ftp.ngdc.noaa.gov/>
  The National Geophysical Data Center (NGDC) of NOAA manages environmental data in the fields of solar-terrestrial physics, solid earth geophysics, marine geology and geophysics, paleoclimatology, and glaciology (snow and ice). In each of these fields it also operates a World Data Center (WDC A) discipline center.  Data and metadata are available.

<URL:http://www.ucar.edu/dss/geo.html>
  National Center for Atmospheric Research (NCAR)'s catalog of geophysical and vegetation datasets.  Several of these datasets are directly available via this page.

<URL:http://ageninfo.tamu.edu/apl-us>
<URL:gopher://ageninfo.tamu.edu/11/apl-us>
  Shaded relief map of USA generated from 30 arc second DEM dataset.

<URL:ftp://ftp.csn.org/COGS/>
  The Computer Oriented Geological Society (COGS) has various mapping-related information, datasets, and software. 

<URL:ftp://spectrum.xerox.com/pub/map/>
  Various USGS and other uncopyrighted data.  Includes USGS DEM and DLG 
files, land use information, and some software to read these files.