UPDATE: Here's another code you can try: N6TRWTV
You can get a free Redbox movie rental if you enter the promo code QM4KTX6 at the kiosk. Remember, this is for a one night rental so return it the next day to avoid being charged $1.
Not sure on when this one expires, so hurry!
Go here to find out which movies are at your local Redbox.
Don't forget to check out the free Blockbuster codes here