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http://librivox.org/ has a collection of growing audio books for free. They are all out-of-copyright. You will find things like Alice in Wonderland and Volsunga Saga.
Thought I would add some other links to update this thread
Most libraries now have downloadable audio books either through Overdrive or One Click Digital. Check with your local library to see what is available (some e-books are available through these as well)
There is a program for young adults called SYNC and every spring they have free audios you can download over a couple of months and you can keep them. You need Overdrive Manager to down load them, which is available through most libraries. I have got a bunch of classics and other stuff over the last 3 years. http://www.audiobooksync.com/
Gutenberg project http://www.gutenberg.org/wiki/Gutenberg:The_Audio_Books_Project
Audio books and poetry https://archive.org/details/audio_bookspoetry