id consider advertising on pandora or other web radio before a pod cast. The problem with podcasts is that they could forward right through the ads if they are saved to their computer or iphone. Pandora forces them in more like traditional radio adverts.
I put it in the Brand Development marketing of a business to do radio, print, and tv ads.
The reason for this is you cannot actively gauge how many customers came from each campaign, as you could with SEM or Telemarketing.
My pecking order (best to least best) is: