Visit the Amazon Video on Demand website and enter the following two coupon codes to receive $3 in video on demand credit for each.
FILMRIOT - $3
HDNATION - $3
To apply the coupon codes, click on any movie/tv title listed on the page (it doesn't have to be one that you want to buy, just select any title). Below the screen that opens, look for the "Have a promotion code? Redeem a gift card or promotion code", then enter the above coupon codes and apply to your existing Amazon account.