Suppliers of GIS Datasets:

Alexandria Digital Library Project, University of California's data site.
• ArcData On-line, ESRI's Internet Mapping and Data Site
• Chesapeake Bay Program GIS Website, provides maps and GIS data pertaining to the Chesapeake Bay and its watershed.
• Digital Nautical Chart (DNC), An "unclassified vector-based digital database containing maritime features essential for safe marine navigation produced by the National Imagery and Mapping Agency (NIMA)". Right now you can only download a sample dataset. Links to other cool data and software from NIMA.
• Earth Science Data EOSDIS Information Management System / IMS / NASA / Global Change Data, "Gateway to over 900 free Earth science data products and services."
• EROS Data Center, Earth Resources Observation Systems (EROS), USGS. Download DEMs, DLGs, and LULCs.
• Food and Agriculture Organization of the United Nations Database, international data concerning agriculture, fisheries, forestry and nutrition
• Geography Network, "access a world of information"
• Georgia Spatial Data Infastructure, Georgia's very own spatial clearinghouse
• GIS Data Depot, "free access to the largest GIS database on the Internet".
• Global Change Master Directory, "a directory of earth science data and services".