In a blender:

1/2 cup vanilla soy milk (or whatever milk you prefer)
1/2 cup low-fat vanilla yogurt
1/2 cup frozen blueberries

and voilà...blueberry smoothie.

I also like to mix frozen blueberries and frozen bananas*; I'm sure there are other good fruit combos for this.

(*when my bananas get too ripe, I cut them into chunks and put them in a container in the freezer, and then use the chunks in smoothies)