Useful for seaching podcast libraries:

Yahoo is testing an audio search engine that can search through over 50 million audio files
on the web, according to the company's sparse online description. Also
listed as sources are independent audio producers and “a collection of
online audio services, such as iTunes, Yahoo! Music Unlimited,
Garageband.com, etc.” Keyword searches return a list of matches, with
artist and title if available, links to web pages with the actual
files, and pricing information for commercial audio. See the
Yahoo Audio Search Help page for more detailed information.