Sound Bible is a resource for finding and downloading free sound clips, sound effects, and sound bites. All of the sounds on Sound Bible are either public domain or labeled with a Creative Commons license. You can find sounds for use in podcasts, videos, slideshows, or other multimedia creations.
Sound Bible is a resource that I discovered by following a link from another resource listed in Mashable's article 26 Places to Find Free Multimedia for Your Blog.
Applications for Education
Sound Bible could be a good resource to have bookmarked for your students to use when they are creating multimedia presentations. I will be adding Sound Bible to my lists of sound resources in Connecting Social Studies and Art Through Video.
Here are some related resources that may be of interest to you:
PodSafe Audio - Sounds for Podcasts
Free Music Archive