LibriVox provides free audiobooks from the public domain. The public domain is any book which is no longer subject to copyright and would tend to be about 70-80 years old although it obviously depends on the copyright agreement.
Anyway examples of the free audiobooks available include Dracula, The Adventures of Sherlock Holmes, Beowulf, Alice's Adventures in Wonderland, Pride and Prejudice, Ulysses and War and Peace. Happy listening!
