Tea is an obvious suggestion, I suppose. I believe black tea has more caffeine, but it is my opinion that green tea tastes better. If you are attempting to lower your sugar intake, you could sweeten the tea with fruit. There are also herbal teas, such as chrysanthemum tea, chamomile, dandelion and all that. People only seem to drink herbal teas to cure ailments, so I'm assuming they prevent the ailments as well. I will close with two tea recipes.
1) Ginger Tea
Place ginger slices and mint leaves in a pot of water and heat until bubbles are rolling, then allow it to steep a few minutes. Add lemon and, if you need it sweeter, a bit of honey. My grandmother drinks this tea for her arthritis and it always smells lovely.
2) Orange Tea
Brew black tea as one normally would when preparing ice tea. The pitcher should be around one part orange juice and three parts tea, or one part orange juice and two parts tea, depending upon your taste. Add a bit of mint, the amount of which also depends upon your preference. I prefer to steep mint leaves with the tea, but you could also use mint extract or even mint sweets if you wanted. Orange juices tend to have quite a bit of sugar in them, I realize, so this tea is more for special occasions.
Good luck on kicking your soda habit.