Does anyone know of a site that lists various open source data feeds or data stores? By this I do not mean OS database applications like MySQL or Postgre, but royalty free sources of DATA. For example, IMDB.com allows you to download their data for free, but it is proprietary and cannot be used for commercial purposes for less than $10k. It would be nice if there was a royalty free version of that somewhere. However I'm looking for any source of data in any industry--entertainment, auto, tech, etc.
Freebase has structured data on approximately 20 million topics or entities.
Freebase is a great option as Osvaldo mentioned, some others that look interesting (haven't personally tested them but have browsed / heard mention of):
Although not a list of useable data sets for free, Some cool data on the federal budget available for the data viz challenge which could be some fun if you're just trying to learn something. Not so useful if you're trying to build something to sell :)
www.datavizchallenge.org/data - sorry for not hyperlinking these - don't have enough rep to do more than two hyperlinks :)