I have started listening to a free audiobook, Singularity by Bill DeSmedt. So far it's great, it's about the real cause of the Tunguska explosion. I'll review the book when I'm done listening to it.

I listen to it as a podcast feed. I had some trouble setting up the feed in iTunes, the response of the podiobooks website was VERY slow, but it did finally work. You can choose to get one chapter per day, per week, or all at once.