Have you tried sponsoring podcasts? I'm really intrigued by that model, but don't (yet) have the funds to advertise on a TWiSt or 5by5.

Sponsorships are really low impact, because they're a distraction to the thing people showed up for (the podcast, the event) and your CTA is by necessity very weak. I am anti-interruption marketing, and not just because it doesn't work.