Use the code BEMINE to get a free rental at Redbox. You may use it one time per credit/debit card. Expires at midnight today - February 14th, 2011.
(You can also send a free Valentine's Day e-card on the Redbox Facebook page to anyone you'd like and it will include this free code for them to use today!)
You will need to swipe your credit/debit card, but will not be charged unless you return it late (after 9pm the next night). In that case, you'd pay $1/day for each day it's late.
Check here for Redbox locations. You can use each code once per credit/debit card.
Other Current Codes: (as far as I know - let us know in the comments how they work for you!)
DVDATWAG (valid only at Walgreens locations)
DVDKROG (valid only at Kroger locations)
DRIVEIN (valid only at Sonic locations)
You can also sign up at their website or text "Redbox" to 727272 to join the redbox text club and get a code for a free rental on the first Monday of the month! (messaging and data rates may apply....yada yada)