The China Debate was put together by Amnesty International to host the discussion about China and human rights during the Olympic games. I can't recall another site that takes the approach that it does -- limiting debate to a few core issues and then building out discussion boards around them. It's a little clunky in this case, but I kinda like it. I suspect actually limiting what people are invited to talk about might paradoxically foster discussion.
I've been thinking a lot lately about how you usefully architect public participation, so that you don't get people all worked up into a froth of excitement until they realize they've just been given busy work or a place to vent, which then ultimately depresses participation. Along those lines, I've been looking into the Obama listening sessions, Get FISA Right, Peer-to-Patent, etc. Anyway, The China Debate is worth checking out -- especially given the news that China has already broken one pre-Olympic promise. (Thx Matt BH)