National Public Radio Offers An Audio Archive

National Public Radio (NPR) offers an Audio Archives that stretches back to 1997.

You can search by keyword and additionally you can narrow your search down to within a certain time period (7 days, 30 days, 1 year, etc.) and by the particular show you might have been listening to.

The NPR Audio Archives are located here: http://www.npr.org/archives/index?loc=hometext.html