What is the safest way to thaw a frozen meat?

The USDA recommends three ways to defrost turkeys: in the refrigerator, in cold water and in the microwave. Never defrost turkey on the counter or in other locations.

• It's best to plan ahead for slow, safe thawing in the refrigerator. Allow about 1 day for every 5 pounds of turkey to thaw in the refrigerator.
• Turkey may be defrosted in cold water in its airtight packaging or in a leak-proof bag. Submerge the bird or cut-up parts in cold water, changing the water every 30 minutes.
• Turkey defrosted in the microwave should be cooked immediately after thawing because some areas of the food may become warm and begin to cook during microwaving. Holding partially cooked food is not recommended because any bacteria present wouldn't have been destroyed.

If you purchase previously frozen meat, poultry or fish at a retail store, you can refreeze if it has been handled properly. 
(Source: Food Safety of Turkey... from Farm to Table. For information on thawing other items, see The Big Thaw - Safe Defrosting Methods for Consumers.