Also I do drink plain seltzer water with a splash of cranberry juice or lemon juice. It has no calories except for the juice you add and you don't need to add very much.
Italian soda is a great low-calorie alternative to artifical-sweetener-ladened "diet" sodas. Soda water (sparkling, or club soda) + a pump or two of syrup.
If you're looking for non-soda alternatives, I agree iced tea and plain 'ole water is nice too.