An example app showing a custom native component in React Native
Example for my article: http://almostobsolete.net/react-native/custom-ios-views-with-react-native.html
WARNING: This no longer works with the latest version of React Native which has removed the createReactIOSNativeComponentClass function in favour of requireNativeComponent. I'll try and get this example and the article updated at some point, but until then here's a commit changing to the new method on one of my projects on Github.