Best place to post design challenges?

I’m looking for suggestions of a good group of sites for posting a design contest. We are currently running an open interpretation challenge and need to find as many websites as possible to get the word out. Anyone have suggestions? The link below is to our challenge page if you need more info.

Crowdspring might be a good place to post your contest but all monetary transactions would have to go through them, along with a fee, I believe.