I drink a can of weak diet soda once a day usually- Sprite Zero. No color, no caffene, no sugar.
My favorite stuff is Powerade Zero, though. It also has electrolytes and B vitamins and I can drink it warm or cold and not have it go flat. I like the blue mixed berry and the orange flavors the best.
I know the artificial sweeteners are reported to be bad for you. But hey, I prefer to die thin.