UPDATE: The TT77TK28 code is actually only working on video games at Redbox, but you can use code SEDF33DD to get a free DVD rental. I just got a DVD using this code!
Through 12/13, you can use code TT77TK28 to get a free DVD rental at Redbox. Currently this code is taking off $3.00, so you can get 2 regular DVDs or 1 Blue-Ray.
These codes work best if you reserve your movies online or using the app, then pick up your movie at the box.