Like Suzanne said, you won't find a "sugar free" yogurt, the best you'll find is no sugar added because of the natural lactose in the milk. I've also noticed the ones that are advertised as "lite" tend to have the most sugar added.
I've found some low fat and fat free yogurts that don't have any sugar added, but they tend to have more calories. I guess it's a toss up on what's more important sugar or calories.
I like the Dannon Fit and light vanilla. It tastes pretty good.
49 years old, 5' highest weight-199lbs
. Started SBD Jan 2004, lost 47 pounds in 6 months, then slowly gained it all back.