Simply Audio Books.com

Simply Audiobooks is a subscription website that allows you to rent CDs and dowload audio books if you are in The UK, Canada or the US.
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More importantly they have some audiobooks for free download including Kafka's 'Metamorphosis' and Jack London's Call of the Wild.

http://www.simplyaudiobooks.com/Free_Audiobooks/dp/202/

The books are downloaded as a zip file (if you have a Mac then stuffit should be able to cope) and are .wma files.

ETA: They also have a potluck monthly free download
http://www.simplyaudiobooks.com/freedownload/dp/109/

it should appears as CD1 and CD2 wma files whereever your down loads appear. This month seems to be 'The Wasteland' by TS Elliott