Podcasts - is there a good place to get good free ones?

Lately I've been listening to "Stuff you should know", and it's actually pretty cool. But I've found the iTunes store to be rather poor when it comes to podcast searching. Most of their material is for-pay. And I'm just not that interested in doing that. Is there a good website/download site for legit free podcasts that is well organized?

Alternatively, is there a good search technique within iTunes to limit it to just the free podcasts? Am I missing a button somewhere?