Xamarin Forms Labs is a open source project that aims to provide a powerful and cross platform set of controls tailored to work with Xamarin Forms.
The Android Holo Colors Generator allows you to easily create Android components such as editext or spinner with your own colours for your Android application. It will generate all necessary nine patch assets plus associated XML drawables and styles which you can copy straight into your project. – See more at: android-holo-colors.com
GitHub has open sourced the Xamarin app templates they use to build apps: http://log.paulbetts.org/open-source-githubs-xamarin-starter-apps/