Update 1st August: I found this too: UCI MAchine Learning Repository http://archive.ics.uci.edu/ml/
Update 12 Nov 2012: I found this! Link to 400 datasets! http://www.datawrangling.com/some-datasets-available-on-the-web
Update 19 Dec 2012: Lynn Langit has a list here: http://lynnlangit.wordpress.com/public-datasets/
Recently on SQL Server Data Mining Forum, I answered a question about where to find DataSets for Business Intelligence Project.
Apart from Datasets AdventureWorks and Contoso data-sets, there are places where you can download data-sets to play with for your Business Intelligence, Data Mining or Data Analysis Projects.
Here is the List of data-sets that I have collected:
3. Windows Azure Data Market
6. Hilary Mason’s Data-Set Bundle: https://bitly.com/bundles/hmason/1 (Also featured in Quora Link that I shared earlier)
7. And If you can’t find the data-set, ask it here: http://getthedata.org/
Have I missed anything? Do comment! I’ll add the link with due credit.