Trimble Navigation http://www.trimble.com
Institute of Navigation http://www.ion.org/
Western Data Systems http://www.westerndatasystems.com
GPS Overview http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html
Topographic Mapping http://www.topographic.com
Frontier Precision Mapping http://www.frontierprecision.com
GPS World Magazine http://www.gpsworld.com
University of Arkansas GPS http://www.cast.uark.edu
National Geodetic Survey http://www.ngs.noaa.gov
Coordinate Solutions, Inc.
http://www.coordinatesolutions.com/