I keep a lot of frozen fruit in the freezer so I can make them at any time. Blueberries, raspberries, strawberries, pineapples, some peaches, blackberries, etc.
Then I use a ripe banana and some yogurt. Fruit flavored yogurts work great. I also have to add some milk to give the blender some help with all that hard fruit. My kids call it "pink drink" and they love it.
During the summer, I make it without the yogurt. But, I add water with some crystal light raspberry mixed in (a half of a single serve packet is enough). This we call "frozen fruit" and I think I like it even more than the smoothies. It is also a great popcicle recipe. Make a big batch and pour what is left into popcicle molds. Very healthy, very good.