Audible has two new freebies available on their site; I found them through the Audible app, so I don't think they are any great secret.
The first, "Agatha Christie: An Autobiography," can be found
here. It says the book is actually narrated by Christie herself, but I haven't listened to it to make sure that is accurate.
The second is "Legion" by Brandon Sanderson, and it can be found
here. This is a science fiction title, and it reminds me a little bit of the television show "The Pretender." It's short, so if you liked the show this might be a good title to experiment with.
Enjoy!
skinmaan
Your audiobook bloodhound