Bud the Teacher mentioned in a post recently two links that every budding podcaster should have bookmarked.
The 3,000 audio clips in unitedstreaming not enough for you? Then you need to check out the FreeSound project, a library of thousands of free sound effects. I can just imagine your heartbeat picking up at the thought of it! There’s a ton to choose from, and most are pretty solid. A few that I checked out were wonky, but that seemed to be the exception not the rule. However, do keep in mind that despite the .edu URL, it is not necessarily ed-safe. There are a few sound clips in there that I’m sure teachers would have some issues with. Like most sites, some degree of supervision is required.
Of course, there’s more to life than sound effects. You also need music! One of my favorites is Garageband.com, because there’s a ton of PodSafe music there. But if you want to do a little mixing and matching to create your own stuff, then visit ccMixter. Thanks to Creative Commons, music on there is kosher to download, remix and then use in your own work. There’s even a few big names like the Beastie Boys on there! In Bud’s own words, "I’m in audio heaven."