Special K protein is the lowest carb cereal I've found, and it's pretty low sugar but not sugar free. If you focus on sugars though, instead of just carbs, there are many low/no sugar options - from cheerios to shredded wheat to the ones mentioned above. I look for cereals with less than 5g sugar per 50g serving...
Beware, many of the Kashis (though not all), and many "healthy" sounding cereals, have as much sugar as frosted kids' cereals