Alpha-lipoic Acid - The university of Maryland Medical Center says: 

Alpha-lipoic acid can lower blood sugar levels, and may help reduce pain, burning, itching, tingling, and numbness in people who have nerve damage caused by diabetes (called peripheral neuropathy). Alpha-lipoic acid has been used for years for this purpose in Europe. 

Cinnamon - A number of recent studies have shown that cinnamon, taken daily with meals, can lower glucose levels, triglycerides, cholesterol and blood pressure. 

Dr. Richard A. Anderson of the Beltsville Human Nutrition Research Center in Maryland suggests diabetics add a teaspoon of cinnamon to their morning coffee, orange juice or cereal. Cinammon is also available in gel caps at most pharmacies and grocery stores. Be sure to observe the recommended dosages.

Chromium - is a substance that improves the effectiveness of insulin. A lack of it can contribute to increased blood sugar levels and insulin resistance. 

Eat foods high in chromium - wheat germ, brewer's yeast, whole wheat, rye, parsnips, apples, spinach and green peppers.

Fenugreek - Fenugreek seeds are being seen to significantly reduce insulin resistance and blood sugar.

Ginseng - Ginseng is a root long used in Asian medicine for a wide variety of problems. Research has shown it to lower blood sugar levels. A recent study showed it to also increase the libido among men who took 500-2000mg a day.

Green Tea - believed to improve insulin effectiveness and reduce  fasting blood levels of glucose. It may also improve the ability of cells to respond to insulin and absorb blood sugar. High in antioxidant properties.

Others include:

Bitter Melon - an Asian vegetable believed to activate an enzyme that is responsible for regulating metabolism and lowering blood sugar.

Mai Men Dong - a Chinese herb for the treatment of diabetes, herbal medicine sites claim research to have shown this herb can stimulate the regeneration of pancreatic beta cells responsible for the insulin production. The regeneration of these cells may help to reverse Type 2 diabetes.

However, tracking down this research is not easy - it's one of those cases where everyone "knows" it's been proved but can't quite show you where.

And on that note, some Good Advice:

Laura Shane-McWhorter, pharmacist, herbal expert and diabetes columnist reminds us: "Just Because Its for Sale Doesn't  Mean Its Safe.

  Although many dietary supplements are considered natural, they have active medicinal properties. Therefore, they may have side effects or could interact with other medications or dietary supplements.

It is important to let your doctor know what dietary supplements you are taking. Sometimes the dose of your regular diabetes medicines may need to be adjusted. It is equally important to let your doctor know if you stop using the supplement.

Do not stop taking your regular diabetes medicines without discussing it first with your doctor.

Use only pure, standardized products from reputable companies. Buy from companies that invest in clinical research and that are willing to answer your questions and show proof from the studies they have done.

Take only one product at a time to determine your bodys response. Evaluate any effect the supplement has on your blood glucose or other indicators of health, such as blood pressure or cholesterol.

Discontinue dietary supplements one or two weeks before surgery, since they may affect blood pressure, interact with anesthesia or cause bleeding. 

Although dietary supplements may help diabetes, they are not miraculous cure alls or substitutes for healthy eating, exercise or medication."