Amazon is currently offering a free movie/tv show download for first time customers of Amazon video on demand (up to $4.50).

Official wording:

A promotional credit in the amount of $4.50 that applies only to Amazon Video On Demand products will be placed in your Amazon Video On Demand account and can be used for any Amazon Video On Demand product, including a movie or TV show. Movie rentals are $3.99 for new releases or $2.99 for library titles (plus tax in some states). This credit expires at 11:59:59 p.m. Pacific Time 7 days