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I have found the following to be very good resources:
Marathon Training Academy - Angie and Trevor Spencer host a very easy to listen to podcast packed with great information. Their web site is loaded with high quality articles and podcasts. Their race recaps are excellent.
Mojo for Running Podcast with Coach Debbie Voiles – Sit down with paper and pencil to listen to these. They are packed with all kinds of useful information.
Trail Runner Nation - A great informal and funny podcast targeting ultra-trail running. But they have a wealth of information covering every aspect of the sport for the everyday runner.