I don't do sugar, so if I use drink mixes they have to have an artifical sweetener in them. The ones I like are the 4C "Totally Light" series - they use sucralose (Splenda) not aspartame.
Not cheap, though - I buy them at a discount store when I can find them.
Another option is unsweetened Kool aid packages, you can add your own sugar, honey, or whatever.
I also like those little dehydrated packages of lemon, lime and orange (can't remember the brand) - no sweeteners, they have vitamin C, and add an interesting flavor to plain water.
Tweak