Update: This deal applies to select other PC digital downloads as well. Some are free, while others may set you back around a dollar.
Square Enix is currently offering a demo for Dungeon Siege III on Amazon that will reward you with $5 in free Amazon Appstore credit just for downloading it. This is virtual money that you can then turn around and spend on any Android apps or games you want (assuming Amazon offers them). Just know that you have to live in the US to take advantage of the deal.
This Appstore credit is different from Amazon Coins. The main issue to be aware of is the impending expiration date. This credit will disappear if you don't use it by the end of July, giving you a little over two months to spend it. But don't worry. Keep hanging around this site and you should have no problem spending $5 of credit in that time.