Census Bureau geographies: Recent TIGER, boundary and geographies files from the US Census Bureau.
IPUMS USA: Census microdata boundaries
National Historical Geographic Information Systems (NHGIS): Historical US Census boundaries from 1790-2010.
Social Explorer (licensed resource) This database for demographic data also has census geographies in the "geodata" section.
BSI National ParcelMap Portal (From Geodata): Tax lot data and geographies for most US counties.
Data.gov:US open government data clearinghouse, primarily for federal agencies. A disparate collection of government data, much of which is in geographic and GIS-ready formats.
Homeland Infrastructure Foundation-Level Data: National foundation-level geospatial data that can be useful to support community preparedness, resiliency, research, and more.
National Archive of Criminal Justice Data (NACJD): Criminal justice statistics at various geographic levels.
National Oceanic and Atmospheric Administration (NOAA) websites
Comparative Climatic Data Publication: Tables of meteorological elements that outline the climate conditions at major U.S. weather observing stations, Puerto Rico, and the Pacific Islands.
Electronic Navigation Charts: Navigation chart data in vector based formats.
Historical Map & Chart Collection (Office of Coast Survey): Historical navigation charts, scanned and georeferenced.
National Centers for Environmental Information: Archive of weather and climate data from US and worldwide stations.
National Weather Service GIS Data Portal: NWS data, GIS formats and web services.
NESDIS Near Real Time Spatial Products: Global environmental data, includes wide array of imagery.
National Renewable Energy Laboratory (NREL): Data resources for a variety of renewable energy technologies.
ProQuest Sanborn Maps Geo Edition (UNI access): digital access to thousands of large-scale fire insurance maps of US cities, searchable by address and GPS coordinates.
ReferenceUSA (UNI Access): Comprehensive US business directory and database. Very rich attribute data includes coordinates. Access available for historical directory with annual snapshots back to 2003.
Safegraph Demographic and Mobility Data: Includes point of interest, foot traffic and mobility datasets. May be available for use through the Data for Academics program.
US Bureau of Transportation Statistics: Portal for GIS and mapping data and projects including the National Transportation Atlas Database (NTAD), National Transit Map, and National Transit Noise Map.
U.S. Energy Information Administration: Broad array of energy related datasets.
US Environmental Protection Agency (EPA) Geospatial Data Download Service: Information on EPA facilities or sites subject to environmental regulation.
US Fish and Wildlife Service Geospatial Data Services
US Geological Survey (USGS)
US National Park Service GIS Data