My kids' favorite recipe:
handful of frozen strawberries (don't have to add ice, water it down)
one kid likes frozen blueberries, one doesn't
one ripe banana (sweetens it! add a little honey if you're out of banana)
big dollup of plain greek yogurt
milk and/or oj, whatever we have on hand
sometimes we add raw spinach - turns it green, boys call it a "sewer smoothie"