I wrote a script to automate the purchase of the free app Amazon put on daily. I've had it running for close to 2 years now and got quite a good collection going.
If you're interested in doing the same, I've cleaned up my code and put it here. Just pip install RoboBrowser, fill in your Amazon credentials, add it to a cron and you're all set.
Nice work and thanks for sharing :) I guess it would also be trivial to modify it to automatically "buy" all the free Amazon Kindle eBooks as well?