NewTalk

This looks like it has been running for a while, but I didn't see it until today: NewTalk. It bills itself as a site where 'experts discuss America's toughest issues.' They take one topic at a time, letting a discussion take place amongst a set of experts spanning the political spectrum as well as the vested interests for the topic at hand (an AARP spokesman on entitlements, etc.). After the discussion period has ended, the discussion closes, and they move to the next topic (and a new mix of experts).

I found it by hitting upon a discussion on addressing entitlement spending that ended in late July: 'Can we afford our entitlement promises? How close is the cliff?' It seems like a pretty worthwhile site with a good mix of participants...