After trying out kindle unlimited, I decided to try out Scribd. Just today they added a whole bunch of audiobooks to the program, and in browsing, I found that Scribd has a lot more titles that I am interested in reading than KU has available.
For example, almost all of Agatha Christie's oevre is available, including A Pocketful of Rye, which I am now reading. In addition, the entire set of Brother Cadfael mysteries - a series that I have been meaning to tackle for ages, is available.
Open Road participates, as do selected books by Simon and Schuster and Harlequin.