You can download free audiobook files of the complete Chronicles of Narnia by C.S. Lewis. These recordings were read by Chrissi Hart for her Readings from Under the Grapevine podcast and are made available by Ancient Faith Radio.
If you don't want to download the audiobook files, you can also listen to the books in your browser.
If you don't already own the books themselves, you can pick up a boxed set of The Chronicles of Narnia on Amazon.com for pretty cheap (make sure you check out the 'used' prices).
HT: Money Saving Mom