About a month ago I succumbed to temptation and bought myself an iPod. I then started looking at podcasts that I could download and found one that I really love. Coverville by Brian Ibbott is a 30 minute show, published 3 times a week, that presents cover music. I have downloaded the entire archive, thoroughly enjoyed listening to it, and have heard many great versions of songs I already knew, as well as some I had never heard before. If you like to hear, different, interesting music I recommend that you check it out.
Note that you do not need to have an iPod or other portable music player to listen to this and other podcasts. They are mostly published in MP3 format so you can download them and listen to them on your computer too.