Podcasts are great for commuting. You get fresh content regularly, on almost any topic out there. I hardly ever listen to music on my iPod, since the only time I really ever listen to music is when I'm at work, and that is really just to help drown out distractions around me.
So, about half of the podcasts I subscribe to are beer-related, and half of those are homebrewing specific. Here is a listing of what I subscribe to. If you know of any other good ones, please let me know.