As of two weeks ago the Amazon Appstore Developer Portal is open for developers to submit their Android apps.
The Amazon Appstore is an alternative to the official Google Market and will enforce stricter rules in an effort to offer a better selection of apps. Pricing will be determined by the developer, but Amazon is free to offer the app for a discount price for example. Amazon already employs sophisticated algorithms in their stores to offer recommendations which could easily applied to the Appstore. It will be interesting to see how the Amazon Appstore will compare to the Google Market and if it will offer a significant advantage to developers.