Free Data Sources

Here's a list of sites I have compiled over the years for free GIS data. Since I work in California a lot of this data is for the State of California. But there are other cool sits if you are willing to hunt a click a little.

Census Data:
http://www.census.gov/geo/www/tiger/tiger2006se/tgr2006se.html
http://data.geocomm.com/tiger/index.html
http://spatialnews.geocomm.com/education/tutorials/e00data/
Raster Data: US
http://seamless.usgs.gov/
http://www.geocomm.com/
http://data.geocomm.com/
http://terraserver-usa.com/default.aspx
California GIS Layers:
http://gis.ca.gov/
http://gis.ca.gov/data.epl
http://atlas.resources.ca.gov/imaps/atlas/app.asp
Digital Raster Graphics: Topo Index
http://archive.casil.ucdavis.edu/casil/maps/drg/index/
TOPOs
http://archive.casil.ucdavis.edu/casil/maps/drg/
IMAGES:
http://archive.casil.ucdavis.edu/casil/remote_sensing/doq/
Satellite:
http://rapidfire.sci.gsfc.nasa.gov/
http://earthobservatory.nasa.gov/Observatory/datasets.html
GIS data hunting guide:
http://www-sul.stanford.edu/depts/gis/web.html
http://gisdata.blogspot.com/
ESRI:
http://www.esri.com/data/index.html
http://www.esri.com/data/community_data/business/index.html
http://www.geographynetwork.com/data/downloadable.html
http://arcgisonline.esri.com/
Coastal Data
http://pacoos.coas.oregonstate.edu/
http://pacoos.coas.oregonstate.edu/esri.html
http://www.csc.noaa.gov/bins/data-standards.html
http://coastalmap.marine.usgs.gov/regional/contusa/westcoast/pacificcoast/gispubs.html
Volunteer Organizations
http://www.angeles.sierraclub.org/GIS/
http://www.scgis.org/