NutriLiving is our main recipe source. We do have some that require fewer ingredients. However, you can also omit any of the ingredients from a recipe to simplify it.
My favorite simple smoothie is spinach, banana, blueberries, walnuts, and almond milk (then I add in some vanilla protein powder every now and then).
In addition, any smoothie recipe you find can be made in the NutriBullet. You may need to reduce the quantity of ingredients from those recipes so that they fit in our cups.
Here is a great site with additional recipes: