I like dandelion greens and cucumber with a stalk of celery. I play it by ear when it comes to amounts, basically: a bunch of dandelion greens, average-sized cuke and celery stalk and about 2-3 cups of water. Some lime juice adds a nice zing, or, if the spirit moves, I'll add whatever I have around that needs to be used up! My smoothie tastes a little bitter, I admit, but I am loathe to add sugar.
Please let me know what you think if you decide to try it!