Pay Per Play places contextual (so they claim) ads on websites; the ads are 5-second audio spots on autoplay. On the one hand, sound has been historically underutilized as an ad medium. On the other hand, autoplay is more annoying than pop-ups. Which probably won't stop the same crowd that places those contextual link ads.
Speaking of which. Contextual links have very impressive click-throughs (I'll have to look at conversion rates, though, since I suspect a lot of the clicks are by mistake), but isn't there a way to tie the ads to key phrases instead of single keywords?