Follow @PEPSI on Twitter.com and tweet to them using hashtag #PepsiMusicNow and you could get a DM back with an promo code good for a $1.29 MP3 credit at Amazon. They aren't sending the codes to everyone, but should be giving away quite a few today.
If you use Fandango for movie tickets, be sure to take advantage of their deal, too, and get $2 in MP3 credits to go with your tickets. It appears to be one credit per purchase, but it's unclear if you can get multiple credits with additional purchases throughout the month.
It appears that if you buy select Android apps (including at least today's free app), Amazon is automatically adding a $1 MP3 credit to your account. I just checked my account and a new credit was there that wasn't there a day or so ago, when I last checked (you can check it by clicking the redeem button from the link below). If you don't have an Android device, you can use Virtual Box (see this Help Page) to create a virtual Android device that can be used to allow purchase of Android Apps from Amazon.
Once you have your code, click HERE to redeem and you can then purchase online or from your Kindle Fire.