Patrick Curran has an article posted on Podcast Help in which he shares the three broad methods of monetizing a podcast. There are no sliver arrows in this article, but Curran accurately summarizes the field.
You'll have to read the article for the full deal, but in short Curran feels that the ways in which podcasts can be monetized fit into three categories:
Commercial sponsorship of the podcast itself
Accepting donations/tips
Monetizing the show blog/website
Personally, I think only categories 1 and 3 have any real potential. I have no faith in people's continuing generosity so while a podcaster may make some money from donations and tips, it's not sustainable.
The other two, however, are exactly the type of thing that many podcast networks (and some independants) are experimenting with. Earthlink and GoDaddy have emerged as heavy podcast advertisers. Almost every podcast I listen to has Earthlink and GoDaddy ads in the show itself and also on the show's website.
