The Adventure Building seminar by WotC at GenCon 2010 was probably my favorite at the time. It was lead by Rodney Thompson and combined the efforts of Bruce Cordell and Chris Perkins where they, with audience participation, built the idea of an adventure.
Be sure to call in with your questions about Dark Sun or Psionic Power and I'd love to hear your GenCon stories. The Tome's Biz-Line is 919-BIZ-TOME or use the widget below.
Noble Knight pick of the episode - HeroScape D&D Set