Every API provider should provide code samples in a variety of languages, helping developers get up and running as fast as possible.
Dwolla is taking this one step further and providing a fully functional iOS app that developers can fork, tweak and use as they wish.
I've talked about what I call "starter kits" before, when I showcased Google+ sample social applications in a variety of languages, but it is still something I don't see from very many API providers.
Complete mobile applications is a great way to showcase what a complete API integration will look like, helping developers see the end goal clearly, while also teaching them best practices.
Do you have any applications you could open source and allow developers to reverse engineer? Or maybe an app you could developer to show developers what is possible!