I wrote a hub about it.
In basics, the one that I have tried and proven to lower blood glucose are
Rose geranium. Raw. Eat 1-2 leaves.
Dry bean pods, boiled like a tea. The taste is not that awful.
Green tea. All forms. Even pills.
Apple vinegar. I am not sure about the mechanism, but it is said to stop liver dumping glucose in the blood stream.
Alcohol. Drank moderately with a meal, can also block the liver from producing too much glucose. (peak level remains low and food is digested slowly).
Raw onion juice mixed with water. Awful taste. Increases insulin sensitivity in the whole body.
Most/all of those will not work on type 1 diabetes. You still need your insulin shots and to count the carbs carefully.