String Theory is a podcast series consisting of several different shows: My First Guitar, Three Chords and the Truth, Alternate Tunings and Gearbox. Each show interviews guitarists about their experiences with the guitar. The most recent episode features Warren Haynes, and some recent past guests are Michael Manring, Keller Williams, Tim Reynolds, George Gruhn, and many more. Upcoming guests include Pepe Romero, Shawn Mullins, Richard Lloyd, Will Kimbrough, etc.
You can listen to the podcasts directly on the String Theory site, or you can subscribe to the podcast via iTunes or any other podcast-capable music player.