Federal Sites
    Federal Web Locator  - Lists all Federal Agencies
 
Department of Interior
    Bureau of Land Management
    United States Geologic Survey
        USGS DLG and DEM Viewer
        USGS Geospatial Data Clearinghouse
        Vegetation Mapping Program
        Retrieving and Unpacking Spatial Data Transfer Standards (SDTS) Data
        SDTS Translation Routines
        Link - MICRODEM
    Fish and Wildlife Service
    Federal Geographic Data Committee
    Department of Agriculture
        National Cartography and Geospatial Center
    Department of Commerce
        Bureau of the Census   - Check out the Subjects A-Z on this website for tons of data sources
            Census Mapper
            Population Characteristic Reports
            TIGER Database and TIGER/Line Extracts
        National Oceanic and Atmospheric Administration (NOAA)

State Sites
    Pennsylvania
        Pennsylvania Spatial Data Access
        Pennsylvania Mapping and Geographic Information Consortium
        Delaware Valley Regional Planning Commission
        Chester County Planning Commission