This is the app which won my patronage Reason: the name (Scarlett reminds me of the Scarlet Letter and Scarlet Pimpernel), the application-icon, and the ability to listen to the eBook.
First the history: Bookle app is developed in collaboration by Adam Engst of TidBITS and Peter Lewis of Stairways Software. The book-publisher / author and software pro programmer combination is hard to fail. The app also features a library interface, allowing you to access your books from the app interface itself. In my list of software to try!
There is a nice video where the features are shown: