So, I'm currently obsessed with smoothies since I bought a bunch of fruit at the store and also went blueberry picking. I've tried all different kinds of smoothies, but so far my favorite recipe is pretty simple:
two big scoops of vanilla yogurt + a handful of blueberries + one banana + two frozen peaches (sliced and frozen by us last year) = best smoothie ever
Smoothies are an amazing healthy snack, both filling and delicious, and you can use just about anything in them, including almost all fruits, vegetables, and various dairy products. Don't worry about adding sugar; it's not necessary since the fruit already has it.
And, since I've been having a smoothie a day for the past couple weeks, I came across this flow chart from Eating Rules and had to repost it. It's awesome, and also gives a lot of ideas for creative smoothie recipes.