Even better, if you already own the book on Kindle it's only $2.99 to add the audio version. You can even buy it on CD from Amazon, if you're into that kinda thing.
This version is narrated by the awesome Kirby Heyborne who does a much better job than the old narrator (me). In related news, Rise of The Circle will be out in audio format later this month. I'll be sure to let everyone know as soon as it's available.