This was shared on another Forum I frequent (yes I do two time Aximsite, different requirements, differnet sites)
http://www.audiobooksforfree.com/screen_main.asp
From what I can tell msot are public domain with a few newer titles added in. I have only downloaded a couple so far but there is a wide selection.
Oh and it is a legaly free site so no one should get their panties in a WAD about me posting something from the Dark side.
Enjoy