Check out One On One Flavors. They sell water soluble and oil soluble flavors.
A few years ago I bought a variety of the water soluble flavors for making flavored sparkling water at home. I've enjoyed most of my choices and the few I don't care for are still interesting (and useful for cocktail experiments).
Some of the cola flavorings are fine as-is. Some of them rely on a bit of sweetness to taste like they should.


I've tried a few extracts. Blending with other flavors they're pretty good. Solo is hit or miss. Real vanilla bean extract is excellent (if one likes vanilla) but ones found on the same store shelf which use vanillin are... Unpleasant.
I've had some success using bitters as well. Angostura makes an orange bitters that mixes well with the oooflavors cream soda flavoring. It's like a creamsicle's older brother turned into a fizzy water. That one gets a nice lift from a bit of honey or agave but doesn't require it.