I have used with success nuun (www.nuun.com). It has a hint of lime flavor. Very pleasing. Because it has no sugar, you can pour it over your head if you start to overheat during a race and is the only thing you carry.
Another one I will be trying is Electro Mix by the Alacer company (makers of emergen-C) (http://www.iherb.com/electromix.html)