National Geologic Map Database: https://ngmdb.usgs.gov/ngmdb/ngmdb_home.html
The Map View can be used to access scanned geologic maps, but they are georeferenced images only (no vector or raster data).
The Topo View can be used to access topo maps for a range of dates, but they are georeferenced images only.
Indiana Geological Survey: https://igws.indiana.edu/
Geologic Data (1:250,000 scale) can be added to IndianaMap and downloaded: https://maps.indiana.edu/index.html
Indiana REST Service Endpoints: https://maps.indiana.edu/arcgis/rest/services
Ohio Geological Survey: https://ohiodnr.gov/wps/portal/gov/odnr/discover-and-learn/safety-conservation/about-ODNR/geologic-survey
Ohio REST Service Endpoints: https://gis.ohiodnr.gov/arcgis/rest/services
D = Department; GS = Geological Survey, NR = Natural Resources, OG = Oil & Gas, OW = Water, MRM = Mineral Resource Management, OIT = Office of Information Technology
Kentucky Geological Survey: http://www.uky.edu/KGS/
KGS Mapping Service: https://kgs.uky.edu/kygeode/geomap/
KGS Mobile App (opens in web browser, not downloadable app): https://kgs.uky.edu/kygeode/geomap/
Kentucky REST Service Endpoints: https://kgs.uky.edu/arcgis/rest/services
Wisconsin Geological Survey: https://wgnhs.wisc.edu/
Has no interactive data viewer nor REST services. All maps or GIS data must be downloaded.
Illinois Geological Survey: https://isgs.illinois.edu/
Illinois REST Service Endpoints: https://data.isgs.illinois.edu/arcgis/rest/services
No dynamic web viewers, but downloadable maps.
USGS LiDAR Explorer: https://apps.nationalmap.gov/lidar-explorer/#/
An easy to use web app that allows you to view where LiDAR data are available in the US. You can then download the LiDAR data directly (LAS files) or you can download the derived DEM.
Open Topography: https://www.opentopography.org/
A large collection of high resolution topographic data (DEMs) as well as access to LiDAR point cloud data if you have a university email.
Indiana Geospatial Information Consortium: http://igic.jinha.org/
This web app run by IGIC provides download access to the LiDAR data flown for the entire state of Indiana in 2013 and 2018.
TopoView: https://ngmdb.usgs.gov/topoview/viewer/#4/40.01/-100.06
Provides fast & easy access to current & past topo maps of varying scales. Can be quickly viewed at high resolution & offers download options in multiple formats.
The National Map Downloader: https://viewer.nationalmap.gov/basic/
Has both current and historic Topo Maps
Boundary files (governmental boundaries, boundaries of major features such as airports, etc.)
Elevation datasets (1/3 arc second is highest nationwide resolution, but has 1/9 arc second for some areas as well as other elevation data)
LiDAR datasets (many of the same as are available through Open Topography
Hydrography (watershed boundaries & streams)
National Agriculture Imagery Program (NAIP) aerial imagery (1 m to 1 ft resolution)
Topo Map data (contour lines, transportation features, etc. which can be added to a different map)
Transportation (roads)
National Map Rest Services: https://viewer.nationalmap.gov/services/
Rest service options for almost all the data downloadable from the National Map.
US Census TIGERweb REST Services: https://tigerweb.geo.census.gov/tigerwebmain/TIGERweb_restmapservice.html
Contains much of the polygon areal units used at various scales throughout the US.
Multi-Resolution Land Characteristics: https://www.mrlc.gov/
National Land Cover datasets along with land cover change assessments for CONUS.
US EPA Environmental Data Gateway: https://edg.epa.gov/metadata/catalog/main/home.page
USGS Earth Explorer: https://earthexplorer.usgs.gov/
This is the largest single source for free satellite imagery available.
Sentinel Open Access Hub: https://scihub.copernicus.eu/dhus/#/home
Provides access to data from all 3 Sentinel missions (only 2 is available through EarthExplorer). Can be tricky to get the data so check out a description of how to download it here.
NASA EarthDATA Search: https://search.earthdata.nasa.gov/search?m=15.639676518650207!30.871582031250004!7!1!0!0%2C2
Has many satellite products and many derived products for many platforms & instruments.
NOAA Data Access Viewer: https://coast.noaa.gov/dataviewer/#/
Access to three principle types of data: Imagery, Land Cover, and Elevation datasets (focused around coastlines including the Great Lakes) that are not available elsewhere. Ex. Coastline LiDAR flights!
Digital Globe Open Data Program: https://www.digitalglobe.com/ecosystem/open-data
There are no free high resolution satellites, but data from Digital Globe has been made available for disaster & humanitarian relief instances (ex. the Beirut explosion). That data can be downloaded at this link & if a project area is open ended, this could be a good source.
UNAVCO Synthetic Aperature Radar Data: https://www.unavco.org/data/sar/sar.html
SAR data from the UNAVCO consortium which is great for showing deformation (if you know how to use SAR data & interpret an interferogram).
US National Park Service Rest Services: https://mapservices.nps.gov/arcgis/rest/services/
Historic NOAA Data: https://libguides.library.noaa.gov/c.php?g=822716&p=5872663
Climate Data Online: https://www.ncdc.noaa.gov/cdo-web/
Severe Weather Data & Storm Events: https://www.ncdc.noaa.gov/data-access/severe-weather
Drought Information: https://www.cpc.ncep.noaa.gov/products/Drought/
NSF National Ecological Observatory Network (NEON): https://www.neonscience.org/data-samples
Great Lakes Commission GIS Data: https://www.glc.org/greatlakesgis
IPCC Data Distribution Center: http://www.ipcc-data.org/index.html
UC Berkley List of GIS Data for Natural Sciences: https://guides.lib.berkeley.edu/gis/natural-science
UNEP Environmental Data Explorer: http://geodata.grid.unep.ch/
US EPA EnviroAtlas Data: https://www.epa.gov/enviroatlas/enviroatlas-data
SFU List of Geospatial Data for Ecological Restoration: https://www.lib.sfu.ca/find/other-materials/data-gis/gis/ecological-restoration
Nature's List of Data Repositories: https://www.nature.com/sdata/policies/repositories