Earthcore by Scott Sigler is a novel that was originally published via podcast. I subscribed to it in iTunes and I've been listening to it. It's not a great novel, but it's pretty fun. For me it's been worth the free download. The author reads it and releases a new chapter (or group of chapters) every week. Actually he finished podcasting Earthcore and ended up getting a publishing deal. So now there's a print version and another podcast novel on the way. If you have some time to kill in a commute or something, subscribe, download the episodes and give it a listen. Find out more at scottsigler.net/earthcore.