Findaway Voices is a distribution conglomerate for audiobooks. They have the widest reach and will get your book listed on most online retailers who sell audiobooks. Their new services include deals to split your royalty with audio producers so you can have the professional design of your book, but they also have the ability for you to list your book with files you have brought, whether you created them yourself or if you had them professionally made from another source. The best part is Findaway Voices is free to list and allows you to set your audiobook prices.
The audio file specifications are the same as ACX, so if you have creating (or having created) your audiobook files, you can list them on either service. Findaway has a boost in royalty if you go exclusive, but they also have great rates for non-exclusive distribution.