This is an interesting listing created by Bernard Marr. I would add the following great sources:

• DataScienceCentral selection of big data sets - check out the first itemized bullet list after clicking on this link
• Data sets used in our data science apprenticeship - includes both real data and simulated data - and tips to create artificial, rich, big data sets for testing models
• KDNuggets repository
• Data sets used in Kaggle competitions

Source for the picture: click here

Bernard's selection:

1. Data.gov 
2. US Census Bureau 
3. European Union Open Data Portal 
4. Data.gov.uk 
5. The CIA World Factbook 
6. Healthdata.gov 
7. NHS Health and Social Care Information Centre 
8. Amazon Web Services public datasets 
9. Facebook Graph 
10. Gapminder 
11. Google Trends 
12. Google Finance 
13. Google Books Ngrams 
14. National Climatic Data Center 
15. DBPedia 
16. Topsy 
17. Likebutton 
18. New York Times 
19. Freebase 
20. Million Song Data Set 

Read original article with description for each data repository.

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