Links to other GIS data sources

Census:
ESRI TIGER Census 2000 data interface
National Historical Geographic Information System-aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2000
United States Census Bureau TIGER
Data for Decision: Three part series (short) of Canada's Land Inventory Geo-Information System

Elevation & Benthic:
ASTER DEM-higher latitude than SRTM data (registration required–free)
Consortium for Spatial Information (CGIAR)-filled global 90m SRTM data
USGS CLICK LiDAR viewer-PA las files are being posted here but not complete
NOAA Digital Coast–coastal and nearshore benthic data sets including LiDAR
Open Topography LiDAR portal
Puget Sound LiDAR Consortium-LiDAR data for Washington and Oregon
Digital Elevation Data

Imagery:
NASA Goddard Space Flight Center Global Change Master Directory
University of Maryland Global Land Cover Facility–LANDSAT and other satellite imagery

Maps-historic and otherwise:
Ask the Cartographer
ArcGIS online Standard Map collection (free for non-commercial use)
new ArcGIS resource center (Groups > ESRI Data and Maps, 17 pages of data)
David Rumsey historical map collection
East View Geospatial-great source for hard to find geologic maps-will scan and georeference from their collection
Historical GIS Boston 1775
USGS Energy Resources maps
Physiographic Provinces of US map
Landsat Image Mosaic of Antarctica
Reed-Bush Geologic Map of US
King-Beikman Geologic Map of US
Geologic maps of all US states 
NASA Earth Observations 
Natural Earth 
World geologic map online viewer 

Others:
National EPA Geospatial data page
National Operational Hydrologic Remote Sensing Center
National Snow and Ice Data Center
USDA National Resources Conservation Service Geospatial Data Gateway
Color Brewer: Color selection tool for visualizing quantitative data out of Penn State 
STEM: Geospatial Technology Curriculum Page
ESRI GIS Education Community 
United Nations Environment Program 
World Clim - Global Climate Data 
NASA data, with lessons and some online analysis capabilities 
SHELDUS, U.S. hazard data set