UPDATE: If you haven't done this yet, it works! I just used the FREE $5 credit on my latest Amazon purchase!
Here's how you can get a totally FREE $5 Promotional Credit at Amazon!
Go FREE $5 Amazon Promotional Credit when you download a FREE game from this page!! What a great freebie-- get a FREE app and a FREE $5 Amazon credit!!
This may be for select Amazon members, so if you don't see the offer at the top of the page, you may not qualify. Also, try it on your desktop computer; I'm not sure if it will work on mobile devices!
The $5 promotional credit is valid through February 2016.
I did this and immediately received an email confirming the credit after downloading the app!
Download one of the below games from Underground and receive a $5 credit on applicable purchases. Not all select games may be compatible with your device. Terms and Conditions apply. Offer valid for US residents only until December 24 at 11:59PM PST.