Like this debate over on the Epic site. I like the fact it has a simple motion, easy voting system and provides the opportunity to comment (columns need a bit more width though).
Debates make for great comment – they divide and get people hot under the collar. You either agree or disagree so it is simple to make a decision.
The comments enable people to expand on the nuances that might get lost in the vote.
Finally, a good thing to have during the summer if you are finding it hard to generate content.
[H/T Clive Shepherd for pointing to this]