Community
FilteredElementCollectors are your friends.
For all views:
Document doc; List<View> views = new FilteredElementCollector(doc).OfClass(typeof(View)).Cast<View>().ToList();
For all 3D views:
Document doc; List<View3D> all3DViews = new FilteredElementCollector(doc).OfClass(typeof(View3D)).Cast<View3D>().ToList();