On Google Play you can download the MP3 "American Pie" by Don McLean for free! I don't know how long their free songs last.
Right now on Amazon Local you can score a $3 Amazon MP3 Credit for FREE!
Thanks to Adventures of a Thrifty Mommy
You can get a $1 MP3 credit at Amazon when you buy certain apps from the Amazon App Store. There's this FREE Rope Rescue App you can get that's part of the promotion. Get a free app and a $1 MP3 credit!!
Thanks to It's Hip to Save