Redbox has a new promo going on through 12/31. If you rent 3 movies, you'll get 1 Free! Rent 5 and get 2 Free! Just make sure to use the same credit card and email address when you check them out. You'll recive an email on January 5th with the promo code for the free rental(s), which will be good through January 16.
Go here for more info.
(Thanks, Smart Couponing!)