This company makes sparkling mineral waters with flavors added, but no sweeteners. They taste good and are very refreshing. You can get them at Costco in bulk for cheap.
Another option is just sparkling water, a splash of lemon juice and splenda, if you need that sweetness. Some iced herb teas have a very sweet flavor because of the spices added, without any added sweeteners, too. Iced chai is delicious and you don't have to add the milk and honey