Surely there are many missing. So please help build a complete and up to date list of social music sites, if you can. Drop a comment.

If you are on the look out for free audio stuff, don’t know exactly what you are looking for, or simply like perusing non-preview audio in wav and aif format, then perhaps free-loops is a good destination.
There are bundles of different audio available, some useful some not that much.
The biggest problem with free-loops, is the [...]