I use a website called iStockphoto when I need to find some good images for a website I am designing. And I usually have good luck finding something that will work.
Yesterday, I received an email from iStock and I learned that they do audio, too. They call it iStockaudio and you can find all kinds of royalty free music at fairly inexpensive prices. It could be a great place to find audio for your next website's flash or even for YouTube videos. It has potential. It only seems that searching for the right audio clip would be the hard part.