When I'm craving soda I'll usually reach for some Kombucha, which is a fermented tea with natural flora/healthy gut bacteria, so it's great for digestion, immune system, UTIs etc. It still has ~1 TBSP of sugar per 500mL (required to cause fermentation) but that's alot better than a Coke, which has ~65g of sugar for the equivalent volume! Tastes great, lots of health benefits, and it's pretty expensive so you won't drink too much =P
Prefer a brand called Rise up here in Canada, but there's another large co called GT's which I believe is available in the States.