Drink diet soda, you won't get fat.
Yeah - no. If you're the type of person who has to drink some crappy-tasting version of a a beverage so that you can have something sweet 24/7 instead of practicing *gasp* moderation, then I don't care how few calories are in that can. Eventually you're going to eat your way to a lard-ass in other ways.
Best to give up soda completely or have the real stuff much much less. Me, I'll have a 12 ounce real soda once a week (if that) and it tastes like a rare, tasty treat rather than some foul, knock-off necessity.