A few data sets are accessible from our data science apprenticeship web page.

• Source code and data for our Big Data keyword correlation API (see also section in separate chapter, in our book)
• Great statistical analysis: forecasting meteorite hits (see also section in separate chapter, in our book)
• Fast clustering algorithms for massive datasets (see also section in separate chapter, in our book)
• 53.5 billion clicks dataset available for benchmarking and testing
• Over 5,000,000 financial, economic and social datasets
• New pattern to predict stock prices, multiplies return by factor 5 (stock market data, S&P 500; see also section in separate chapter, in our book)
• 3.5 billion web pages: The graph has been extracted from the Common Crawl 2012 web corpus and covers 3.5 billion web pages and 128 billion hyperlinks between these pages
• Another large data set - 250 million data points: This is the full resolution GDELT event dataset running January 1, 1979 through March 31, 2013 and containing all data fields for each event record.
• 125 Years of Public Health Data Available for Download

You can find additional data sets at the Harvard University Data Science website. I was particularly interested in their LinkedIn data set. KDNuggets is also a great resource, and for more, check out this link. 

Cross-disciplinary data repositories, data collections and data search engines:

• http://usgovxml.com
• http://aws.amazon.com/datasets
• http://databib.org
• http://datacite.org
• http://figshare.com
• http://linkeddata.org
• http://reddit.com/r/datasets
• http://thedatahub.org alias http://ckan.net
• http://quandl.com
• Social Network Analysis Interactive Dataset Library (Social Network Datasets)
• Datasets for Data Mining
• http://enigma.io

Single datasets and data repositories

• http://archive.ics.uci.edu/ml/
• http://crawdad.org/
• http://data.austintexas.gov
• http://data.cityofchicago.org
• http://data.govloop.com
• http://data.gov.uk/
• http://data.medicare.gov
• http://data.seattle.gov
• http://data.sfgov.org
• http://data.sunlightlabs.com
• https://datamarket.azure.com/
• http://developer.yahoo.com/geo/g...
• http://econ.worldbank.org/datasets
• http://en.wikipedia.org/wiki/Wik...
• http://factfinder.census.gov/ser...
• http://ftp.ncbi.nih.gov/
• http://gettingpastgo.socrata.com
• http://googleresearch.blogspot.c...
• http://books.google.com/ngrams/
• http://medihal.archives-ouvertes.fr
• http://public.resource.org/
• http://rechercheisidore.fr
• http://snap.stanford.edu/data/in...
• http://timetric.com/public-data/
• https://wist.echo.nasa.gov/~wist...
• http://www2.jpl.nasa.gov/srtm
• http://www.archives.gov/research...
• http://www.bls.gov/
• http://www.crunchbase.com/
• http://www.dartmouthatlas.org/
• http://www.data.gov/
• http://www.datakc.org
• http://dbpedia.org
• http://www.delicious.com/jbaldwi...
• http://www.faa.gov/data_research/
• http://www.factual.com/
• http://research.stlouisfed.org/f... 
• http://www.freebase.com/
• http://www.google.com/publicdata...
• http://www.guardian.co.uk/news/d...
• http://www.infochimps.com
• http://www.kaggle.com/
• http://build.kiva.org/
• http://www.nationalarchives.gov....
• http://www.nyc.gov/html/datamine...
• http://www.ordnancesurvey.co.uk/...
• http://www.philwhln.com/how-to-g...
• http://www.imdb.com/interfaces
• http://imat-relpred.yandex.ru/en...
• http://www.dados.gov.pt/pt/catal...
• http://knoema.com
• http://daten.berlin.de/
• http://www.qunb.com
• http://databib.org/
• http://datacite.org/
• http://data.reegle.info/
• http://data.wien.gv.at/
• http://data.gov.bc.ca
• https://pslcdatashop.web.cmu.edu/ (interaction data in learning environments)
• http://www.icpsr.umich.edu/icpsrweb/CPES/ - Collaborative Psychiatric Epidemiology Surveys: (A collection of three national surveys focused on each of the major ethnic groups to study psychiatric illnesses and health services use)
• http://www.dati.gov.it
• http://dati.trentino.it