In Visual Studio 2012, my Xamarin for Android Intellisense was missing when trying to edit Android .axml files. This is a nightmare for me, since I have no idea of the Android namespaces.
I found the answer with a bit of googling and basically if you open one of the .axml files, or any .xml file Visual Studio will display the XML menu. Go to the Schemas option and select Add, then browse to one of the following locations (depending on which version of windows you’re running).
Windows 32 bit:
%programfiles%\MSBuild\Xamarin\Android Windows 64 bit:
Two .xsd files should be shown
schemas.android.com.apk.res.android. Simply add these two files and Intellisense should start working correctly.