This German site is awesome- tons of great games, including a lot of the ones we talk about on the show that you can play online for free.
http://www.brettspielwelt.de/Spiele/The only thing is that it's a bitch to navigate because the defaults are all in German. And even beyond that, it's just a bitch to navigate.
This page however really helps explain how to download the client and what to change in your profile to make it easier to work.
http://www.boardgamegeek.com/thread/77942I have a couple of profiles on the site (one per computer- not intentional) but I'd love to sign in with other folks from here and play Dog or Dominion with you all.