I've made grapefruit(awesome with gin)
Orange vanilla, which was ok,
Strawberry, which was a hit with the kids and tasted super fresh
I'm currently waiting for a batch of ginger "ale" which I made with a basket full of ginger, pink pepper corns, lemon, brown sugar and a pinch of chilli flakes
I also make water kefir, which ends up as a healthy version of pop. I've done lime, raspberry, guava(my favorite), pomagranite and mixed berry.
I have all the herbs on order for a batch of root beer, using the recipe from nourished kitchen, which I'm pretty excited about.
I basically put together a base of whatever flavors I feel like trying, make it slightly too sweet, then carbonate and refrigerate.