I recently started having green smoothies, and this is the best recipe I have found so far.
http://ohsheglows.com/2011/01/13/classic-green-monster/
Hope that helps!

1 scoop chocolate protein powder, 2 cups spinach, 1 cup milk of your choice, 1 frozen banana (about 4 oz), sprinkle of stevia and a tsp of cocoa powder (unsweetened). Looks like baby poop, tastes like a milkshake!