Data.gov http://data.gov The US Government pledged last year to make all government data available freely online. This site is the first stage and acts as a portal to all sorts of amazing information on everything from climate to crime.
US Census Bureau http://www.census.gov/data.html A wealth of information on the lives of US citizens covering population data, geographic data and education.
Socrata is another interesting place to explore government-related data, with some visualisation tools built-in.
European Union Open Data Portal http://open-data.europa.eu/en/data/ As the above, but based on data from European Union institutions.
Data.gov.uk http://data.gov.uk/ Data from the UK Government, including the British National Bibliography – metadata on all UK books and publications since 1950.
Canada Open Data is a pilot project with many government and geospatial datasets.
Datacatalogs.org offers open government data from US, EU, Canada, CKAN, and more.
The CIA World Factbook https://www.cia.gov/library/publications/the-world-factbook/Information on history, population, economy, government, infrastructure and military of 267 countries.
Healthdata.gov https://www.healthdata.gov/ 125 years of US healthcare data including claim-level Medicare data, epidemiology and population statistics.
NHS Health and Social Care Information Centre http://www.hscic.gov.uk/home Health data sets from the UK National Health Service.
UNICEF offers statistics on the situation of women and children worldwide.
World Health Organization offers world hunger, health, and disease statistics.
Amazon Web Services public datasets http://aws.amazon.com/datasets
Huge resource of public data, including the 1000 Genome Project, an attempt to build the most comprehensive database of human genetic information and NASA ’s database of satellite imagery of Earth.
Facebook FB +0.65% Graph https://developers.facebook.com/docs/graph-api Although much of the information on users’ Facebook profile is private, a lot isn’t – Facebook provide the Graph API as a way of querying the huge amount of information that its users are happy to share with the world (or can’t hide because they haven’t worked out how the privacy settings work).
Face.com: A fascinating tool for facial recognition data.
UCLA makes some of the data from its courses public.
Google Public data explorer includes data from world development indicators, OECD, and human development indicators, mostly related to economics data and the world.
Junar is a data scraping service that also includes data feeds.
Buzzdata is a social data sharing service that allows you to upload your own data and connect with others who are uploading their data.
Gapminder http://www.gapminder.org/data/ Compilation of data from sources including the World Health Organization and World Bank covering economic, medical and social statistics from around the world.
http://www.google.com/trends/explore Statistics on search volume (as a proportion of total search) for any given term, since 2004.
Google Finance https://www.google.com/finance 40 years’ worth of stock market data, updated in real time.
Google Books Ngrams http://storage.googleapis.com/books/ngrams/books/datasetsv2.html Search and analyze the full text of any of the millions of books digitised as part of the Google Books project.
National Climatic Data Center http://www.ncdc.noaa.gov/data-access/quick-links#loc-clim Huge collection of environmental, meteorological and climate data sets from the US National Climatic Data Center. The world’s largest archive of weather data.
DBPedia http://wiki.dbpedia.org Wikipedia is comprised of millions of pieces of data, structured and unstructured on every subject under the sun. DBPedia is an ambitious project to catalogue and create a public, freely distributable database allowing anyone to analyze this data.
New York Times http://developer.nytimes.com/docs Searchable, indexed archive of news articles going back to 1851.
Freebase http://www.freebase.com/ A community-compiled database of structured data about people, places and things, with over 45 million entries.
Million Song Data Set http://aws.amazon.com/datasets/6468931156960467 Metadata on over a million songs and pieces of music. Part of Amazon Web Services.
UCI Machine Learning Repository is a dataset specifically pre-processed for machine learning.
Financial Data Finder at OSU offers a large catalog of financial data sets.
Pew Research Center offers its raw data from its fascinating research into American life.