If you're looking for something to listen to at work or otherwise, I've recently discovered a site that allows you to download a buttload of old radio programs:

http://www.otr.net/

There's some great stuff on there for those interested. I've been wearing out Abbot and Costello. That stuff is a lot racier than you might think it would be. The double entendres abound. And it's sponsored by Camel!

And then there's Orson Welles' radio work:

http://www.mercurytheatre.info/

Orson was the master. You can listen to his classic War of the Worlds broadcast (look out Kokomo!) and everything else. The beauty part is that all this stuff is out of copyright and therefore quite free.