SoundCli.ps is a gallery of free sounds that I just learned about from Stephen Ransom. SoundCli.ps is a community-powered site on which you can upload sounds to share and download sounds shared by others. I was able to download sounds without registering on the site. To upload sounds you do need to register on the site. The video below gives a short overview of the site.
Applications for Education
If you're looking for a new source of sounds that your students can use for their multimedia projects, SoundCli.ps might just be what you're looking for. Remind students that they should credit the source of the sounds that they download and use in their projects.