Today you can get a $3 Amazon Instant Video credit from Amazon by tweeting!
This offer ends tonight at midnight PST and then you have until May 31st to use the $3 credit.
You can definitely find one to rent for free or cheap with the credit but if you want to buy here are some I found that would cost you under $2 with your credit. You can see all of the movies available at Amazon Instant Video.
Eat Pray Love $4.99
Pure Country $4.49
Ice Age $4.99