Sorry to hear you are diet drinker. In my opinion, diet drinks are a farce, and when drunk in large quantities defy thier given 'purpose'.
I usually drink any of a great variety teas I have, mostly without any sugar, but I will put a tiny pinch of salt, to enhance the taste of the tea, if it hasn't been made wrong. I also have one or two of either cranberry, pomegranate, white grape juices, or apple cider on hand. I'm a big fan of water, I prefer to filter it at home, and reuse a store bought bottle I've had for years now; instead of going out and buying bottled filtered water from the store. I drink organic whole milk and organic soy milk, alternating the two in my breakfast cereal and chocolate milk.
But, as much as I am a health nut, and looking for ways of improving my diet I cannot for the life of me ever see myself buying flavored and colored waters, or diet anything. It's more a matter of taste I suppose. I'm not against them really... diet sodas just make me burp, a lot!