My other 'alf likes these, and she never adds sugar, just adds fruit in.  Avoiding processed sugar is a good thing .

Another good one I'm happy with

Ingredients:
1 cup fresh or frozen pineapple
2 small cucumbers
2 cups fresh spinach
½ frozen peeled avocado
1 orange, peeled
½ lemon juice squeezed into the blender
1 cup filtered water

Optional additions:
1 handful of fresh mint