The chart below is a recent Consumer Product Safety Commission draft release of their testing of various manufacturer's drywall for sulfur gas emissions from Chinese Drywall. All drywall tested was regular 1/2" drywall (from 4'x8' and 4'x12' samples) except for the one sample described as 3/8". All the samples they tested were untreated. Both Chinese and North American samples were obtained by the CPSC from various sources, as a part of its ongoing investigation.
Two symbols need explanation:
^ This sample was collected in China and is not believed to have been imported into the United States.
* This is a sub-sample tested that was known to be imported from China into the U.S. in either 2006 or 2007.
The testing was conducted by the Lawrence Berkeley National Laboratory and published in March 2010.
You will notice that the manufacturers and labels thought to be problems turn out to be the ones with terrifically high hydrogen sulfides, and other gaseous discharges, which are what cause corrosion to metals and medical problems. There were rumors that American-made drywalls were also causing problems, and that turns out not to be the case. They are testing as safe. That would follow since we have been using American-made drywalls since World War II and have never before experienced the recent problems with Chinese products.
My recommendation: When you buy drywall, or consult with your builder as to which drywall will be used on your house, look on the back side (or the edge if two pieces come together) to see the stamps or manufacturer logo. It seems you are safe with American brands.