iOS: Audiobooks are great, but they're generally pretty expensive. Fortunately there are a ton of free audiobook recordings in the public domain, and now you can easily download them to your iPhone, iPad or iPod Touch.
Audiobooks is a very simple app. You browse or search for books you want to listen to and download them directly to your iOS device for playback. Skipping through parts is really simple, plus you have basic controls for moving throughout the part of the book you're currently playing.
While Audiobooks offers a bunch of free titles, you can also grab premium versions if you're willing to pay. You can do this on a per-title basis or just pay $8.99 for unlimited. Audiobooks also sells material that's not in the public domain under the Professional heading, so there's a decent variety of content available.
The downsides really come with the interface, which — in the free version — is full of ads. It's a very busy interface in general and not the best-looking app you'll find for iOS. That said, it makes acquiring and listening to free audiobooks very, very easy, and it's not that big of a deal once you get more acclimated to the app.
Audiobooks is a free app for iOS and is available right now.