In-app billing is now live for Android. In-app billing allows developers to sell virtual goods or even upgrades from within their own apps. As an example, one of the apps that launched with in-app billing is Tap Tap Revenge. In this case, users will now have the ability to purchase extra songs.
In-app billing gives developers additional methods to monetize which is great for the consumer because more developers will create their magic for Android. [Android Developers]
There are several other apps that are now taking advantage of in-app billing: