Dad's Old-Fashioned Root Beer, "America's Premium Root Beer" is produced by the Monarch Beverage Company and has been around since 1937 (though maybe as early as 1933), where it was developed in Chicago. Its essential ingedients are licorice(anise), vanilla, and wintergreen. It is distibuted mainly throughout the Midwest, and I haven't seen it from New Orleans to Florida. I have found it in Texas and Western Louisiana, and I assume it to be available in Georgia, since Monarch Beverage Company is based in Atlanta. Dad's was the first beverage to ever use the six-pack format, which was invented by the Atlanta Paper Company in the 1940s.
As a root beer connosieur, I'd have to say that this is one of my favorites. As well as the very plain blue/red/yellow label, I enjoy the distinctly sharp taste that comes from the anise and wintergreen, and the following smoothness from the vanilla. This is also the closest I can find to homemade root beer made from root beer extract. It just has a very sassafrassy taste. Many root beer fanatics criticize the sharp anise taste, but I enjoy it very much, as well as the lax carbonation, which makes it very smooth and refreshing, as opposed to giving me gas. Course, I don't get to burp much, but then again, that's what Coca-Cola is for.
DoubleD points out that it is also available in some parts of New York State.