I use ZYM tablets. They're kind of like NUUN but don't have any sugar alcohols (at least the lemon lime flavor...there is a new orange one I haven't looked at and a berry one with caffeine).

I won some, so I tried them out, and they really help in the summer and for indoor workouts. In the summer, I really need the extra electrolytes, but I will get stomach distress from drinking too much of my sports drink with sugars. So, I'll have one bottle with calories and one with Zym (and maybe one with straight water to dump ONTO my body). Zym in one bottle and the rest plain water is enough for most of my indoor workouts to keep me from getting headachy, but if it's a long one, I might add a gel.