We have a site to allow users of apps to pay using Paypal and Amazon (mobpaynet.com - Android Piracy Protection, In-app purchase, Subscriptions, and More!). It's an SDK based platform used as an in-app purchase. It opens the app to new countries that Google Checkout does not offer. It also has a much wider user base (Paypal and Amazon have very large user bases). We also offer different types of app payment options. You can setup subscriptions, time based (non-recurring subscriptions?), or feature unlocks (unlock all or portions of your app). Still in Beta and basically trying to see of folks are interested. Check it out at mobpaynet.com, free to sign up. Let us know if this is something you find useful.