Fantastic repository of free content audio samples
The Freesound project is a site where you can download (and contribute) sound samples, recordings, noises and all sorts of audio snippets. The beauty of the site is that everything is released under the Creative Commons Sampling Plus License (you can view the license here). To paraphrase from the license - this means you are free “To sample, mash-up, or otherwise creatively transform this work for commercial or noncommercial purposes.” Wicked!
Now, keep in mind that the site isn’t just a massive repository where you can leech tons of useful sounds. There is a thriving community too, where once you create an account you can interact with other sound artists.
All in all, it’s an awesome resource, you could spend months trawling through the available sounds. Just make sure you do something creative with them! 
Check out The Freesound Project here.