NPR has made available podcasts of their Intelligence Squared (US and UK) debate series, summary from their website:
“Intelligence Squared U.S. brings Oxford-style debating to America-- one motion, one moderator, three panelists for the motion and three against. Past topics have included religion in America, Hamas, and Hollywood.”
The format is as follows: The audience (who purchases tickets to the debate), prior to entering the hall, is polled on their positions on the motion being put forward (“Is George W. Bush the worst president in 50 years,” “Is it worth the cost of lowering carbon emissions,” etc.) and the results announced at the start of the debate. Expert panelists are invited to argue for or against the motion (Karl Rove and William Kristol argued against the former), and the winners are determined by which side swayed the concluding poll in their favor (Rove and Kristol reduced the number of those who agreed that Bush was the worst in 50 years, therefore winning the debate). Below is a sample of what debates are available for download:
Should We Accept Steroid Use in Sports?Should America Be the World’s Policeman?Are Tough Interrogations Necessary?Should We Legalize the Market for Human Organs?Is The Government Responsible For Health Care?Do Guns Reduce Crime?Does Google Violate Its ‘Don’t Be Evil’ Motto?Is Bush The Worst President Of The Past 50 Years?Is Reducing Carbon Emissions Worth The Cost?
Think of it as the Lavender Room, but with posters who actually know what they’re talking about, and know how to make a salient point without the discussion devolving into simian shit-slinging or Palin-Obama bashing. 
You can find the podcast’s website here: http://www.npr.org/templates/story/story.php?storyId=6263392 or by searching itunes for “Intelligence Squared”
I highly recommend the Bush legacy debate, for starters.