I just yesterday stumbled on Monster's Ultra Zero 0 calorie beverage. Amazingly enough its delicious. Almost a grapefruit flavor to it.
The red and blue Ultra flavors are good too.
But usually diet drinks are a waste of money, IMO.
I'm a big fan of the Monster Rehab line, or at least the few I've tried. 10 calories, which is just right. Enough natural sweetness for the character, then mostly just artificial.
I'd prefer to see more use of Stevia. I think Pepsi and/or Coke has or had a Stevia-sweetened drink, and they both jointly developed the most popular options (Truvia and PureVia). Problem is, I just rarely look at the drinks aisle (I'm a water or beer kind of guy), but I swear I never see the drinks marketed as using Stevia.
And those are, for the large part, the only drinks with Stevia. Few actually go and just put it on the back ingredient label, not drawing any attention.
I want to see Coke and Pepsi make their best formulas with Stevia. As a possible example, Coke Zero: replace with all Stevia in the formula for that, don't give a new "Coke Zero with Truvia" name or draw attention on the can to the change. Advertise it at first ("We switched to a natural sweetener! Hope we appreciate it.

"), but that's it.
Everyone will accept it, we'll all be happy, you'll still be filthy rich. It is a, dare I say it, win/win for us all! Yay! Now please, get to work so you can take my money.
Thank you,
destrekor
P.S. A new product idea: take Coca Cola - replace sugar with stevia, though you could also do a blend, with perhaps 3g of sugar, or thereabouts, and the rest Stevia and perhaps some sugar alcohols. A true Coke-syrup light formula with more natural sweeteners.