UPDATE: Audible has upped their initial offer to two free audiobooks when you first join!
I've posted this offer every summer for the past few years and people seem to enjoy it despite the credit card hurdle, so if this is something you might enjoy, have at it!
Every summer I go to a music festival or two with my friends and family. This year that entailed a 24-hour roundtrip car ride which would have been greatly enhanced with a free audio book download in my opinion. Seems like it would have been the perfect solution to end the 90 minute argument my brothers and I had over which starter Pokemon was the best. It's a small miracle everybody who departed with us made it back home now that I think about it.
I want to point out you have to use a credit card to sign up. You get the free audiobook with a 30-day trial. You can cancel anytime during those 30 days and you won't be billed a cent. However, after 30 days, they'll charge you $14.95 a month. Here are the details on how to cancel your free trial if you choose to do so.