At Amazon, get an $3 Amazon Instant Video Credit for free when you link your Twitter and Amazon accounts. (If you're not already signed in, you'll be prompted to do so; afterward, you'll automatically tweet a message that will qualify you for the discount.) That's the largest free Amazon Instant Video credit we've seen. (We've seen several hassle-free credits for other Amazon departments in recent months; those were as high as $2.) Deal ends May 2 at 2:59 am ET.