I forgot to say *IMPORTANT* that you're supposed to keep the temperature always above 110º (that's why the yogurt machine is so handy since you don't have to worry about that part).
The smoothies I make go like this: 1 cup of yogurt, a whole bunch of fruit (strawberries, mixed frozen berries, blueberries - frozen or fresh or bananas), ground flax seeds (I have a coffee grinder for them next to the blender), a scoop of protein powder (I use GNC's chocolate Whey protein but you can get it at the grocery store and you can use Soy protein too), a couple oz. of water to make it grind smoothly and some ice.
You can also use honey as a sweetener; my Mom likes that. You don't have to use protein powder but I think it makes it more filling. Flax seeds are good for you and this is an easy way to add them to your diet - they add a nutty flavor.