I've been listening to podcasts lately. They are just mp3 files, so you can listen to them on any mp3 player, you don't have to have an iPod. I use a MuVo. Podcasts cover a wide spectrum, from material that sounds like a professional radio show all the way to "some guy ranting into a two-dollar microphone." Here is a brief guide to some of my recent discoveries.
IT Conversations has a lot of interviews about technology. Try the one about real money in virtual economies.
Coverville is a music show about cover tunes. There is one episode that is all about Madonna covers.
The Sci Fi Channel has a great series of Battlestar Galactica podcasts that go along with the new series. Each podcast actually syncs up with a specific episode of the show, so you can listen to them while watching the show, kind of like a DVD "commentary track." This is such a great idea, I wish more shows would do this.
WC Radio has a series of shows about the game World of Warcraft. You can listen to these live or get the archives.
Gadling has a bunch of podcasts about travel, including interesting interviews.
Dawn and Drew are a married couple who do a quirky podcast together. In this episode, Dawn decides to try to boost the ratings for their podcast by having sex with Drew on the show. Things don't go entirely as planned, with humorous results. Warning: this one is adult content and not for the easily offended.
Cinecast is all about movies.
There are also some podcast directories you can use to find podcasts of interest, such as Podcast Alley, Podcast.net, PodcastPickle, and Podcastdirectory.com.