InfoGuides: Big Data & Geovisualization: Data Resources

Data Repositories and Discovery

Data.gov: a portal to find datasets published by the US governments covering geospatial data.
ArcGIS Open Data: discover and download data hosted by ArcGIS Open Data repository.
EarthData (EOSDIS) by NASA: interactive browser to view and download global base layers including real-time satellite imagery. See also Historical Earth Data Archive Site.
Geobrain (Remote Sensing Data Products, GMU Online Repository): Landsat, MODIS, ASTER and NASA ECHO data.
Healthdata.gov: search the U.S. health care data and download recently added big datasets with the API.
Land, Atmosphere Near real-time Capability (LANCE): NASA Real-time Data and Imagery.
National Climatic Data Center: access to U.S. climate and weather datasets from satellite or land-based stations.
NCAR (National Center for Atmospheric Research): Earth Science data portal for NCAR and UCAR (University Corporation for Atmospheric Research (sponsored by NSF).
NOAA Science on a Sphere: a discovery took for NOAA repository for air, water, snow & ice, land and more.-check also National Ocean Archive System (NODC).
NGDC (National Geophysical Data Center of NOAA): access to bathymetry, global relief, national hazard,solar event, geomagnetic data, etc.
NSIDC (National Snow and Ice Data Center): access to scientific data for glaciers, ice, snow, and more.
SEDAC (SocioEconomic Data and Application Center): multi-disiplinary datasets including remote sensing (hosted by CIESIN at Columbia University).
US Census Bureau: access U.S. Census data and tools for visualizations.
USGS Real-time Data: Earthquakes, Water, Floods, Geomagnetism, Remote Sensing and Landsat. Volcanoes, Droughts, & more.

DataOne: a world-wide DataNet repository community to share Earth Observation data
Data.gov.uk: a portal to find datasets published by the UK government departments covering aerial imageries and geospatial data
Earth Online: Earth observation data distributed by European Science Association.
Earth Server: Big Earth Science data provided by multi-sources in EU.
European Union Open Data Portal: A major portal to find EU datasets across topics
Gapminder World: get fact-based worldview data (WHO or WB) and links to the data provider
NHS Health & Social Care Information Centre: UK national health and social care data
Unlocking the Landsat Archive: raster data archive via Australia.
World Meteorological Organization (WMO) Data: world weather, climate, and water data.

Amazon Web Service (AWS) Public Datasets- contains huge public datasets including Tiger/Line, US Street Vector Data, NASA's database of satellite imagery of Earth.
Facebook Graph API: Get data in and out of Facebook's social graph.
Twitter Developers: access to samples of the live tweets by the streaming APIs.

Related Useful Resources

Geospatial and GIS Infoguide (via Mason): GIS data resources in general.
Data & Digital Scholarship Services (DDSS): Various services related to data, GIS and statistical analysis.
Citing Data Infoguide (via Mason): Guide for citing datasets.
Open Geoportal: A consortium catalog for geospatial data offered by many academic institutions in the U.S.
CIC Geoportal: A consortium catalog by big ten universitites in the U.S.
IRI/LDEO Climate Data Library: Data repository including analysis tools for climate-related data.
UNAVCO's GEON: Portal for imagery, strain & seismi, troposoheric data and other web services.
Data Science Central: Online resources for big data practitioners covering analytics to data integration to visualization.
Publicly Available Big Data Sets (via Hadoop Illuminated): Lists selected big data repositories.