I ended up picking up Scales Margarita mix at the grocery store and it was ok. It tasted a little saccharin-y for my tastes so I probably won't buy it again unless it's the only thing around.
Next stop was the Master of Mixes Lite Margarita Mix. I liked this one a good deal better than the Scales Mix. It had a traditional Margarita taste so although I knew I was being good, it didn't taste like a diet margarita.
To be honest, I still haven't tried Skinny Girl BUT I did ship several bottles to our new place so that I could try it when we get there :). I have heard lots of good things about it from girlfriends, mother/sister in laws, etc so I have faith it will be tasty.
For a quick run down on the dunlop WON'T be getting with these drinks, you can reference the calorie count below: DRINK UP BEEOTCHES! (and for those of you who don't know what a "dunlop" is, you can find the definition at urban dictionary)
Skinnygirl Margarita - 100 calories per 4 ounces (Calories are higher because Skinnygirl has built in Tequila!)
Master of Mixes - 20 calories or fewer per 5 ounces
Scales Margarita Mix - 5 calories per 4 ounces
By the way, you should also note that most of these companies offer different flavors of their lighter fare. For instance, Master of Mixes has Lite Strawberry Daiquiri and Lite Sweet and Sour Mix. Scales has the same plus a Bloody Mary Mix. Skinny Girl just released a line of Sangria. All of them sound pretty darn good to me!!