Right now you can use code: ACME26 to get a free rental at any Redbox location. This can be used once per debit/credit card, so you can rent more than one for free by using different cards! Expiration date is unknown.
To use the code, select ‘Rent with Promo Code’ before selecting your movie.
Don’t forget that you can also use codes DVDONME, BREAKROOM, and DVDATWAG (Walgreens only) once per debit/credit card to score a free movie as well. If you live near a Giant PA, read here how you can get a free rental code.