Any ideas how I can promote my Mystery Contest more?

Hi all...I run a fun Mystery Contest on my site, Listasaurus.com, and initially we had some good participation with it (secret weapon doing some free ad posting out there in cyberspace).

But, I'm looking for new ways to promote this to get new people involved. I have some Google Adwords running, but not getting too much that way, and honestly it just costs us too much. The contest is kind of our loss leader on Listasaurus, just something that's a bit fun for folks to do, and help keep them interested in the site.

Here's the link to the contest, and I'd love to hear suggestions if anyone can think of low-cost ways to get a buzz going on this.

Thanks!!