Here are 2 sites that I came across:
1. soundsnap.com seems to be free from copyright issues. From their site:
Soundsnap is the best platform to find and share free sound effects and loops- legally. It is a collection of original sounds made or recorded by its users, and not songs or sound FX found on commercial libraries or sample CD's. It was originally started by a small group of sound people from all over the world. Our common belief is that sounds and samples should be free for everyone to use in their projects, commercial or not.So basically if you have some unique sounds or loops, you can contribute in the above site too. I created a couple of loops in the FL Studio demo version software. I am planning to share them in the above site. By the way, the FL Studio software is awesome.
2. findsounds.com on the other hand searches for audio files hosted by Web sites throughout the world. So there are bound to be copyright issues. From their site:
When you perform a search using FindSounds.com or the WebPalette feature of FindSounds Palette, you obtain links to audio files hosted by Web sites throughout the world. The sounds in these audio files may be copyrighted and their use governed by national and international copyright laws. We do not offer advice on the fair use of these files. In compliance with the United States Digital Millennium Copyright Act of 1998, we will remove links to copyrighted sounds from FindSounds.com and FindSounds Palette at the request of the copyright holder. Such requests must be made in writing and identify the specific links to be removed.Let me know if you find more such sites.
Here is another site that I came across:
3. freesound.org is a collaborative database of Creative Commons licensed sounds. Here is the license: http://creativecommons.org/licenses/sampling+/1.0/.