From Yahoo! Answers on how to profit from podcasting – adverts are mentioned of coure as well as paid content:
The acid test is “if this were a book, would I be prepared to pay for the content?” if the answer is no then there is no point trying to sell the podcast. Best way is to get a loyal audience base first and offer some samples, then try to sell the podcasts from there.
Like anything else: exclusive content, micro-audience, loyal fans.