The freebies are all classic/older books, search the market for audiobooks, i've tried a few and they're all similar.
If you want current books, the only one I've used is Audible. You do pay per book and you do pay a monthly fee, sort of (I did a free trial and when I went to end it, I was offered several deals through the cancel process and wound up taking one that was $10/year plus books).