Audible is having a
3-books-for-2-credits sale, through March 29 at 11:59 p.m. PT; members only.
It looks to be a pretty good selection in the usual categories (general fiction, mystery, romance, SF, general nonfiction, history, bios, self-help, YA). My impression after skimming the choices is that there are fewer retreads and many more books I don't recall seeing previously in the credit sales.
(I especially recommend
Special Topics in Calamity Physics by Marisha Pessl.)