Sample Android Xamarin Studio project which uses Nutiteq 3D Maps SDK for Android (http://www.nutiteq.com)
Shows basic mapping functions - define base map (online or offline), add layers (vector, raster, 3D) and objects on map
Sample code: MIT license.
Nutiteq SDK - commercial license. Free OpenStreetMap license is also available. See http://www.nutiteq.com for details.