Look into Infinit Nutrition. You can make up your own sports drink. You get to decide the amount of electrolytes, the composition of the carbs - fast vs slow metabolizing, whether or not you want protein, and the amount of flavor. They make it very easy to set up your mix and, if needed, they will discuss it with you by phone. I've used it for a couple of years and swear by it.
www.infinitnutrition.us.

Oops, I missed that someone else already mentioned this. It's worth saying again IMHO.