If you're a podcaster, you may want to take a look at Fruitcast. They've created a service that puts ads into your podcasts so that you can make money, much like what Adsense does for websites. They say:
Want to earn income from your labor of love? Putting ads on your podcast is now as easy as signing up for an account and changing the URL of your podcast's RSS feed.
If you don't know what podcasting is, wikipedia has a good entry.