At Amazon, get a $1 Amazon MP3 credit for free with the purchase of select Android Apps. With many apps offered for free, that's among the best such offers we've seen for an MP3 credit from Amazon. (We saw a free $1 Amazon MP3 credit in October, but that required Facebook.) Some free apps eligible for the credit include Pandora, Kindle, Angry Birds Seasons Free, and more. Offer ends December 31, and the credit expires January 31, 2014.