Random House is offering 3 free audio books when you sign up to receive their monthly newsletter by email. These books are unabridged stories in MP3 format. To get your free downloads, go to this link and follow the directions in the upper right hand corner.
Survival by Louis L'Amour - this appears to be a short story just over 1 hour in length.
White cat by Holly Black
read by Jesse Eisenberg
approximately 6 hours
Nate the Great Goes Undercover by Marjorie Weinman Sharmat
read by John Lavell
approx 13 minutes