I've been working on a low carb coffee Frappuccino for a while. My wife and I have been on a very low carb lifestyle since the beginning of the year and I was very disappointed to find out how many carb are in the "lite" frappuccinos at Starbucks. This recipe works great for me, I have not tried any flavored variations since the plain coffee frappuccinos are my favorite.

1 cup cold coffee (I keep my leftovers in a jug in the fridge for iced coffee)
1 pack Starbuck's instant (optional) if you like a strong coffee flavor
1 cup crushed ice (as our Samsung fridge dispenses it)
1/4 cup half-n-half
1/2 teaspoon xanthan gum
4 tsp Splenda (adjust to taste)

Combine and blend. I use a "blendtec" blender on the 'smoothy' setting, it is a very powerful blender so ordinary hamilton beach (etc) blenders may not do a great job. Xanthan gum should be well known to low carbers but if you don't know about it you should find some. I've seen it in most but not all grocery stored, usually in the section that has the odd grain and baking ingredient section like spelt, corn meal, flax, etc. Last time I tried Trader Joe's they DIDN'T have it but most "health food" stores do.