FreeSFX is a repository of free sound effects. Enter a search term or browse the categories, and preview and use the sound effects in your A/V projects. Most sound effects are available as MP3s or WAVs.
AudioTool allows you to create and mix your own music, generated from a range of tools that you select and plug in, complete with cables. Each tool looks and operates like its real life counterpart, enabling great levels of control and creativity for your students.
Dig.ccMixter is a community music site featuring remixes licensed under Creative Commons where you can listen to, sample, mash-up, or interact with music in whatever way you want. This is great material for podcasting. If you're into sampling, remixing and mash-ups grab the sample packs and a cappellas for download and you can upload your version back into ccMixter, for others to enjoy and re-sample.