I've mentioned this before but Podcastclicks.com brought close to 27,000 cliks to podcasters in the two years it was online. I took it offline because of some issues with my hosting (it was bringing in soe badnwidth, and their support was horrible).
I've brought it back online with a system in place to help cover the cost of bandwidth.
If you go to www.podcastclicks.com you can sign up now through 3/1/08 for $10 a year for UNLIMITED usage. If you compare this to any kind of google adsense campaign your running you will clearly see how this is a much better value. After March 1, the price goes to $20 a year.
What is podcastclicks.com? Its a banner exchange program for podcasts (and only podcasts). You upload a banner on your server, set up an account at podcastclicks.com and let the system know where you put yor banner (standard sizes, 120X120, 120X240, 468X60). Then you copy some code and put it onyour website/blog. Now every time you show a banner, someone will show YOUR banner. You can measure how many clicks you have received, and see which of your banners ae doing the best.
Then go to www.podcastclicks.com to get started.