I mostly drink berry-based smoothies when I do, but have recently started experimenting with even crazier "green" shakes. These shakes are rich in vitamins A and C and usually contain a lot of dietary fibers.
Here is a recipe I've put together for myself after researching which ingredients are often used in green smoothies.
Basic green smoothie
1 banana (good base for almost any smoothie, whether berry or green)
1 large handful of fresh spinach
1 cup of water (or add cucumber)
A few tablespoons of protein powder (whey, soy etc.)
Mix in a blender of sufficient size. Depending on your taste, at least ginger and kiwi also work well with this.