Redbox distributes a code every Monday that you can use for 1 free rental. The code expires tonight at midnight.
The code for today is: D9P24G
To use the code, do the following: on the first screen select "Rent With Promo, enter the code, choose your movie and swipe your debit or credit card (this is in case you don't bring the movie back. They will put a $1 charge on your card to hold the movie, but if you return the movie by 9 pm the next day, the charge will be removed). You can use 1 code for each debit/credit card that you have, so to rent multiple movies, just do the above process with each card.
Thanks to Nicole at frugalisfab.blogspot.com!