I like using bananas as a base regardless of what flavour combo I choose. It makes it creamy without having to use milk or yogurt. Strawberries, raspberries & blackberries are good together. Mango, pineapple & passion fruit is another. Banana & date. Pear & apple. Melon is nice in the summer. Kiwi & lime. Apple & ginger. Pretty much any fruit you like will work! You can thin it out with water or apple/orange juice if it's too thick.
Is there a particular reason you don't want veggies in there? If it's a matter of flavour, you won't be able to taste a handful of spinach or a piece of cucumber. Beetroot works well in berry smoothies and you can add avocado instead of banana for the creamy texture & healthy fats.