Amazon is giving away another $5 Instant Video credit to anyone with a Twitter account. All you have to do is click the banner above, then click the big yellow Tweet and Get $5 button - the prompts will lead you thru the rest of the process, including linking your twitter account with your Amazon account. The credit applies to your account instantly (but will expire on October 31, 2011 if not used).
Note that Twitter is currently overwhelmed, it appears, so if you get an error message, just refresh the offer page at Amazon and try again. It took two tries with mine. Once you get a green success message on the screen, you can click thru to any Instant Video item and use the "View Balance" link at the bottom of the big black "box" on screen (right next to "redeem a gift card..").
Fine Print: Offer good from August 29, 2011, 10:00 AM PST to September 2, 2011, 11:59 PM PST, for those in the US only. Other restrictions may apply (see offer for details).