Just a simple PopupMenu sample.

Main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <Button
        android:id="@+id/MyButton"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="Click Me!" />
    <ImageView
        android:layout_below="@+id/MyButton"
        android:src="@android:drawable/ic_menu_gallery"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/MyImageView"
        android:layout_alignParentRight="true" />
    <TextView
        android:id="@+id/MyTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click me as well!"
        android:layout_centerInParent="true"
        android:layout_centerVertical="true" />
</RelativeLayout>

popupmenu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android">
  <group android:id="@+id/group_popupmenu">
    <item android:id="@+id/menu1"
        android:title="Popup menu item 1"/>
    <item android:id="@+id/menu2"
        android:title="Popup menu item 2"/>
    <item android:id="@+id/menu3"
        android:title="Popup menu item 3"/>
  </group>
</menu>

PopUpMenuSampleActivity.cs

using Android.App;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace PopUpMenuSample
{
    [Activity(Label = "PopUpMenuSample", MainLauncher = true, Icon = "@drawable/icon")]
    public class PopUpMenuSampleActivity : Activity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            SetContentView(Resource.Layout.Main);

            var button = FindViewById<Button>(Resource.Id.MyButton);
            button.Click += (sender, args) => ShowPopupMenu((View)sender);

            var imageView = FindViewById<ImageView>(Resource.Id.MyImageView);
            imageView.Click += (sender, args) => ShowPopupMenu((View)sender);

            var textView = FindViewById<TextView>(Resource.Id.MyTextView);
            textView.Click += (sender, args) => ShowPopupMenu((View)sender);
        }

        private void ShowPopupMenu(View v)
        {
            var popupMenu = new PopupMenu(this, v);

            popupMenu.MenuInflater.Inflate(Resource.Menu.popupmenu, popupMenu.Menu);

            popupMenu.MenuItemClick += (sender, args) => Toast.MakeText(this, string.Format("Item {0} was clicked", args.Item.TitleFormatted), ToastLength.Long)
                                                              .Show();
            popupMenu.Show();
        }
    }
}

Nice example Cheesebaron....very helpfull