If you purchased certain kindle ebooks on Amazon you may have a credit.
Click here to check if your Amazon account has a credit for Kindle ebook purchases. If you purchased certain ebooks from 4/1/10 and 5/21/12 you may qualify.
The credit works almost like a gift card, you don’t have to use it on Kindle eBooks. You do have to use it on items sold by Amazon, not third party sellers.