If you have a Redbox near you, take advantage of these free rental codes! Other ways to save are to complete your first online reservation and to sign up for their texts (you will get a free rental code the first Monday of every month).
REDBOX - Good for first time users only (verified)
DVDATMAC - Good only at McDonalds
DRIVEIN - Good only at Sonic
DVDATSONI - Good only at Sonic
DVDATWAG - Good only at Walgreens (verified)
WALMART - Good only at Walmart
GAMEFAN1 - Good for a free game rental
I have verified some of these for myself. Let me know if a code does or doesn't work for you or if you know of other free codes!