I personally use Netflix, but this deal is almost too good to pass up. Today first-time users can enroll in a six-week trial of Blockbuster by Mail ($26 value) for free!
Just go to Blockbuster.com, sign up for an account, and use the promo code groupon. Pay attention to the expiration date, though! If you forget to cancel your subscription at the end of trial period, your account will automatically renewed and charged for a month of service.
You can read the terms and conditions here. Enjoy!