Audible US is having a 3 for 2 credit sale on trilogies and there is plenty of great content available. Normally audiobooks cost one credit and each credit costs $15. Three books for two credits makes the cost of each audiobook $10, which is a great deal. I would recommend the Passage trilogy by Justin Cronin and read by Scott Brick.
Michael Kozlowski is the Editor in Chief of Good e-Reader. He has been writing about audiobooks and e-readers for the past ten years. His articles have been picked up by major and local news sources and websites such as the CNET, Engadget, Huffington Post and Verge.