I downloaded the "Audible for Android" app onto my LG Ally phone this morning. I've already got both Kindle for Android and Aldiko on it, but I decided to try out the Audible app since I'm a long-time Audible member and have a bunch of books in my library there.
It seems to work pretty well. It's like the Kindle app in that you can download books from your library as you need them, then delete them off of the device to save space when you've finished listening. It has a sleep timer, which is a big plus for me since I like to go to sleep listening to a book. And finally, it works great through my bluetooth earpiece. That's handy when I'm somewhere that I need to pretend to be paying attention!