you can play around with the proportions and adding water (or sparkling water) or herbs to most any of these. Parsley, tarragon, thyme go unexpectedly well here and there depending on your tastes. And a pinch of salt, celery seed, or hot pepper (or just a mild jalapeno) can sometimes pick up a too bland vegetable mixes pretty well. Obviously some will be better to different pallets than others :)
apple, pear, kiwi
strawberry, banana
strawberry, pinapple, banana
strawberry, pineapple
blueberry, lemon (this one takes a little futzing with)
blueberry, kiwi
blueberry, mango
raspberry, kiwi
kiwi, pear
kiwi, pear, watermelon
kiwi, pear, lime
cantaloupe, strawberry
cantaloupe, banana
tomato, parsley, garlic
tomato, apple, parsley
tomato, apple, celery
tomato, beet, carrot
tomato, bell pepper
tomato, celery, dandelion (very important to make sure it’s not bitter)
orange, lemon, dandelion
cucumber, mint
cucumber, pear
apple, carrot (not one I particularly liked)
apple, sweet onion, just a dash of fennel seed or nutmeg (I didn’t make this one, a friend did and she want’s to add cabbage too; I think the onion really needs to be sweet)
Lychee could be added to pretty much all of those and the ones @Hypocrisy_Central mentioned (seed removed of course).
Peach is another I neglected that works well; just peach sparkling water and a dash of kiwi or cucumber can be refreshing.
Also play around with different varieties of each fruit, different stages of ripening, and seasonal/canned things; korean pears for example tend to be more lightly flavored and juicy than Bartlett pears, green mango vs. perfectly ripe, strawberries in season vs. peaches from a jar.
Oh and don’t forget grapefruit, I personally detest it, but if you don’t any acidic juice could be subbed with it.