Looks like Yahoo will no longer have a Podcast search, so must move on to other specialized search engines. Looks like the Podcast directory is still up and running as well as of course the itunes store, where one can download free podcasts of NPR material- the key is to get each episode within the week after it's up on the site, after that it's .99/cast of This American Life and the like. Look on wikipedia under podcast and you get a listing of many podcast directories.
I see that the ALA has a podcast of library news, and you can get an rss feed, when the new p-cast comes out. I don't see an easy way to download , but you could listen to it streaming directly from your computer.