For Android I use Poweramp for music and Listen Audiobook for books, which is another excellent audiobook player - costs 75p. It has forward and back scan which you can set the amount of time to suit yourself, chapter jumps, a sleep timer, adjustable speed and bookmark feature. You can also automatically download the book cover to display whilst you are listening. The headphone controls on my S3 work even when the screen is locked. Very pleased with this app but it won't work for DRM'd books, but this can be removed with a bit of twiddling. I don't mind paying for apps if they work, and this one is the best audiobook player I've found so far.
The Audible app for Android is also good, plus you can download your books directly from your library.
