GIS Data

World

ESRI ArcGIS.com = http://www.arcgis.com/home/
DIVA-GIS = http://www.diva-gis.org/gData
Perry-Castañeda Library Map Collection = http://www.lib.utexas.edu/maps/
UNEP Grid = http://www.grid.unep.ch/
NASA = http://earthobservatory.nasa.gov/
NASA Reverb= http://reverb.echo.nasa.gov/reverb/

National

US Government = http://geo.data.gov
US Census = http://www.census.gov/geo/www
PreJoined Census Data = http://www.census.gov/geo/www/tiger/tgrshp2010/2010DP1.html
TIGER = http://www.census.gov/cgi-bin/geo/shapefiles2010/main
USGS = http://earthexplorer.usgs.gov/
USGS Seemless = http://seamless.usgs.gov/
USDA: NRCS Geospatial Data Gateway = http://datagateway.nrcs.usda.gov/
FCC = http://www.fcc.gov/maps
Historical Topo Maps = http://nationalmap.gov/historical

State

TNRIS = http://www.tnris.org/
GLO = http://www.glo.texas.gov/GLO/agency-administration/gis/gis-data.html

Central Texas

CAPCOG  = http://www.capcog.org/data-maps-and-reports/geospatial-data/
City of Georgetown = http://maps.georgetown.org/gis-data/
City of Austin = ftp://ftp.ci.austin.tx.us/GIS-Data/Regional/coa_gis.html
Williamson County = http://wilco.org/CountyDepartments/GIS/Data/tabid/532/Default.aspx

GIS User Forums

http://gis.stackexchange.com/
http://www.arcgis.com/home/groups.html


GIS Education Resources

http://www.teachgis.org/
http://training.esri.com/