Let's just say I was really bad with soda for a while. Switched to diet before realizing that aspartame gives me horrible headaches, then switched back to regular for a time (oh, the calories, the calories) before realizing that I could have non-aspartame diet soda in moderation, either sweetened with Splenda or stevia.
I eventually bought a Sodastream and have used it to make my own carbonated drinks. It took me a while to figure out what worked best for me, but if I really want something fizzy, I'll add a small amount of cranberry juice (not the cocktail kind, but the real stuff with nothing added) to it. Pure cranberry juice is sour, but diluting it with soda water actually hits the spot for me and requires no added sweeteners.
And lately, I haven't been craving soda at all. I actually keep three one-liter bottles of filtered water in the fridge at all times and drink them throughout the day (I refill one and stick it back in the fridge as soon as I'm done with it). The convenience of that has really helped me stick with drinking something healthy and I actually crave my cold water these days.