Last August TuneIn launched a premium package where you pay $8.99 per month to get access to over 40,000 audiobooks. This is a fairly good deal, because you can listen to all of the content you want, without having to pay extra. There is a large segment of users that want to know what titles are in the catalog before they sign up for access. If this is the case, you might want to check out THIS link. It basically lists all of the audiobooks TuneIn has in their library and lists them in order of popularity.