Blockbuster usually has one sale or another on their previously-viewed product, and this is definitely one of the better ones. From now until the first week of April when you buy two DVD’s you’ll get the third one free.
A similar sale is on right now with their previously played games, though there’s no word on how long that deal will be on for.
EDIT: Correction — the game sale is Buy One, Get One 1/2 Price.