reason.com/blog and distributedrepublic.net have intelligent commentators, though reason tends towards the smart-allecky side. You would probably enjoy both blogs if you like the Marginal Revolutions and Overcoming Biases of the world. Oh, and Cafe Hayek.

For legal issues, there's the Volokh Conspiracy. I believe that Eugene Volokh is a libertarianish law professor somewhere.

Is the Becker/Posner blog still around? I believe that both of them have a Nobel prize in Economics.

Greg Mankiw has a good blog, with a good community.

Most of the internet sucks for intelligent discussion. That's what happens when you let any-old-body in.