Free Classic Audio Books is a site where you can download free audio books in either mp3 or m4b audio book format for iTunes and the iPod. They have books such as Pilgrim’s Progress, Treasure Island, War of the Worlds, Swiss Family Robinson, Emma, The Secret Garden, Robinson Crusoe, and many others.
LibriVox provides free audiobooks from the public domain.
The Erskine family offers a free downloadable “Living Books for the Ears” audio program each week at Homeschool Radio Shows. These old time radio dramatizations have been especially chosen for homeschool family listening, and include dramatizations of classic stories & historic biographies. You can sign up for their weekly newsletter.