These are great sources of knowledge and inspiration for game design.
The Story Games Forums
The Story Games Forums have many talented, experienced and helpful members. Discussions are most often constructive and insightful, and keep a high theoretical level. Here is a link to a feedback thread for Anno Daemonum.
Adam Koeble has a lot of great things to say in his live-stream show Office Hours. For me it has been a gift that just keeps on giving!
Sean Nittner’s podcast Narrative Control was my first big entrance to talking about roleplaying game theory. There are loads of ear-candy among these episodes!
Theory from the Closet
Clyde Rhoer’s podcast Theory from the Closet is one that I discovered very recently. The episodes vary greatly in sound quality and overall yappiness, but the content as well as the guests are often very interesting. I’ve had many “aha”-experiences with this one!
Jennifer Wong’s podcast Jennisodes contain a lot of great talk and I’ve enjoyed many of the conversations on the show. Since the original site was taken down it has been a bit difficult to get an overview of what the episodes are about, but you’re in for a treat if you start digging!
Rickard has been of big help when I was delving deeper into game design theory. One of his most influencial threads is called We Know so Little of our Hobby. You can find more of Rickard’s thoughts on game design at Google+. He also has two games in English available for free: Imagine and The Murder of Mr. Crow. Be sure to give them a try!