It's not a syrup, but I like to add a couple tsp. lemon juice to a big glass of seltzer. You could also add a splash of fruit juice of any kind to make a flavored soda water. Nearly 0 calories if you only use a tablespoon or so in a 16 oz glass.
I intend to give up artificial sweeteners as much as possible for reasons I would rather not go into. There is just one small problem. I am a soda junkie. The regular sodas have way too many calories for me, so that isn't an option. Giving up soda will definitely not work for me either. I already have a soda stream system at home (makes carbonated water). My intent is to start making not only my own soda, but my own soda syrups as well using Stevia as the sweetener. Has anyone tried this? Any advice/recipes could be appreciated.