The Snopes link is definitely worth checking out. They debunk the 8-glasses-of-water-a-day myth as well.

Water is indeed good for you. Soda, fruit drinks, non-carbonated soft drinks are all full of empty calories, and cola will make you belch like a cow. There's nothing particularly evil about them beyond that. And Alex is right: your own stomach acid has a far more acidic pH than any cola.

As far as the caffeine goes: Tea has about half the caffeine of regular coffee in a serving of the same volume. A 12 ounce can of cola has about 1/4 the amount of caffeine as that contained in a cup of coffee. Chocolate has even less. It's a commonly held myth that tea and cola have more caffeine than coffee, but it just ain't true.

The caffeine info is from PoisonDex, the national toxins database.