I found this site...
http://www.booksshouldbefree.com/ and it is full of free to use titles. They are all the old out of copyright titles but still so good to listen to old favorites. Right now I am listening to the Edgar Rice Burroughs "John Carter of Mars" series. These books bring back old memories of me reading a chapter a night to my boys at bedtime. It instilled a need to read in them as I found out they were reading ahead during the day because they could not wait till bedtime to find out what happened next. After John Carter we moved on to Tarzan. Oh yes the biases of a century ago do come through but still if you like doughty hero's and brave and beautiful princesses it holds up....no wussy fainting maids here, the princesses are as good with a sword as they are beautiful...The reality that we now can see pictures of Mars as it is does not diminish the lovely fantasy of John Carter's Mars in the books.
There are lots of other types of titles, just in case you are not a science fiction fan, check it out I am sure you will find something you want to listen to.