I've found the perfect way to pass the time while putting the miles in to train to walk my second half marathon: book podcasts. Listening to books seems to keep my mind occupied more than just listening to music. Before I know it, I'm finished with a workout! Currently, I'm listening to The Adventures of Huckleberry Finn, and I have A Tale of Two Cities waiting in the wings.
To find your own free audiobook podcasts, search iTunes. Two of the podcasts I like most are called LoudLit and Audiobooks by Annie.