Here are some Redbox codes for free rentals. Please note that not all codes will work at every location so sometimes you will need to try a few before one works.
WALMART - free rental at Walmart location only
The Redbox Text Club Reward – Text DVD to 727272 to sign up the Text Club and get a promo code good for a free rental on the first Monday of every month via Text Message.
Blockbuster Express Codes - good thru 9/19