Each month christianaudio.com gives away a premium audiobook download for free. While not all of the audio books they offer are worth getting, the free download for the month of October is Spurgeon's All of Grace. (Click the banner to go to the download page.)
After creating a free account and logging in, click 'add to cart' on Spurgeon's All of Grace and then proceed to 'checkout' as if you were paying for it. Then you will be able to use the coupon code OCT2008 to download the audio book for free.