Some of the links got truncated by Quora, so here's the same list (modulo intervening wiki edits) with full URLs:

  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
  http://ckan.net
  http://quandl.com
  http://www.growmeme.com/overview
  http://www.kdnuggets.com/datasets/index.html
  http://enigma.io
  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/geoplanet/data/
  http://econ.worldbank.org/datasets
  http://en.wikipedia.org/wiki/Wikipedia:Database_download
  http://factfinder.census.gov/servlet/DatasetMainPageServlet
  http://ftp.ncbi.nih.gov/
  http://gettingpastgo.socrata.com
  http://googleresearch.blogspot.com/2006/08/all-our-n-gram-are-belong-to-you.html
  http://books.google.com/ngrams/
  http://medihal.archives-ouvertes.fr
  http://public.resource.org/
  http://rechercheisidore.fr
  http://snap.stanford.edu/data/index.html
  http://timetric.com/public-data/
  https://wist.echo.nasa.gov/~wist/api/imswelcome/
  http://www2.jpl.nasa.gov/srtm
  http://www.archives.gov/research/alic/tools/online-databases.html
  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/jbaldwinconnect/DataSets
  http://www.faa.gov/data_research/
  http://www.factual.com/
  http://research.stlouisfed.org/fred2/
  http://www.freebase.com/
  http://www.google.com/publicdata/directory
  http://www.guardian.co.uk/news/datablog
  http://www.infochimps.com
  http://www.kaggle.com/
  http://build.kiva.org/
  http://www.nationalarchives.gov.uk/doc/open-government-licence/open-government-licence.htm
  http://www.nyc.gov/html/datamine/html/home/home.shtml
  http://www.ordnancesurvey.co.uk/oswebsite/opendata/
  http://www.philwhln.com/how-to-get-experience-working-with-large-datasets
  http://www.imdb.com/interfaces
  http://imat-relpred.yandex.ru/en/datasets
  http://www.dados.gov.pt/pt/catalogodados/catalogodados.aspx
  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/
  http://www.icpsr.umich.edu/icpsrweb/CPES/