There are tons of herbals and natural remedies such as Cinnamon that have a definate blood glucose lowering effect. HOWEVER, I wouldn't bet my orals on them SIGNIFICANTLY lowering your blood sugar if you are either a type 2 or type one that is either using insulin or multiple orals to control your blood sugar.
Typically, there is a response to all these herbals, but it is never what people hope for as they are always looking for an alternative to the drugs they are on. I personally have no axe to grind against any of the alternative approaches, but remember, it will not give you a response (in most cases) that will let you drop any of your current medications. Lets say you get a 15% drop in blood sugar from an herbal (and thats huge). If you are at 100 for fasting...that would put you at 75 and thats nice...but not enough to drop the meds that got you to 100 initially. Lets say without meds you run 250 fasting. That same 15% is going to only bring your fasting to 213 and that is WAY out of bounds for healthy blood sugar!
So to sum up, experiment with herbals judiciously, but don't have your heart set on them replacing any of your current therapies!