There is a natural sweetener called Stevia, which can be bought in a powder or liquid form. It's a preferable alternative to artificial sweeteners, but it does have a disagreeable aftertaste.
I used Stevia until I was able to kick the sugar habit. I don't drink diet soda but I did like sugar in my coffee, and my biggest food vice is my coffee drinking. For years, I was also a diet Coke addict. I used to smoke, and I think the cigarettes killed the bad taste of the diet drinks. I can't stand any soft drinks at all anymore - too sweet.