Please post your favorite GIS Data resources with a quick blurb on how
you use them.
Here are mine:
http://seamless.usgs.gov/
DEM, landuse - use the option for defining your coordinates and you
get great results. Make sure you hold down the control key through
the duration of the download process to prevent popups.
http://nationalatlas.gov
You can actually download all of the GIS layers at this site. Pretty
amazing.
What are your favorites?