The SF "Cinnamon Dolce" is super yummy at Starbucks. It's one flavor I can't make myself at home, so it's a fun splurge.
Just be aware of what caffeine can do to your blood sugar, and try to stick to no more than 2 servings a day as Dr. A suggests.
Also, beyond the milk fat issues, make sure you don't get whipped cream or other sprinkles on top. The Cinnamon Dolce latte traditionally has these little sprinkles, so you may have to ask for it without--though when you order it SF, they often know that you don't want them.
Dunkin Donuts also has a ton of flavors and none of them have sugar. But you have to make sure they don't put sugar in the latte/iced latte. I tend to get them in the store so I can watch as I've had them make mistakes with the drive-thru.