Archive . org has free audiobooks for download through its LibriVox Free Audiobook Collection.
From my understanding, the books are out of copyright or in the public domain and read by volunteers. A lot of the classics are there such as The Adventures of Sherlock Holmes, Moby Dick, The Adventures of Tom Sawyer, Pride and Prejudice, Adventures of Huckleberry Finn, Dracula, Alice's Adventures in Wonderland, etc. Almost 10,000 titles are available.