i have used frozen fruit in the past, but it tasted horrible, cranberries, strawberries, blackberries, blueberries the lot of them, but i think freezing kills them.
so it's best to just stick to the basics.
i know a lot of people who don't like peanut butter, but they love it in a shake or chocolate peanut butter flavour protein powder.
you can get cheap vanilla pods off ebay too.
so try banana, half a vanilla pod and some peanut butter and milk. very cheap smoothie there and should taste great
If you don't freeze the bananas i find the smoothie gets too full of air bubbles.