I was on a Bruce Cockburn related site and found a link to this site called etown, which is part of the National Public Radio set-up in the States. There's also an audio archive which you have to register for. I haven't tried that yet

http://etown.org/podcast/

For those of us who like (say it quietly) Americana this is a motherlode. There are dozens of downloadable podcasts of live performances in an archive stretching back to February 2006. A quick skim has revealed shows by Dave Alvin, Neko Case, Ricki Lee Jones, Shawn Colvin, Kathleen Edwards, James Taylor, Chris Smither, Ray LaMontagne, Josh Ritter, Del McCoury, Charlie Louvin, Sarah McLachlan and a load more artists, some I recognise others I don't.

Dive in and enjoy it. If you discover any particularly good shows let us know.