I know that there were more than a few people who found the labels "good source of whole grains" and "excellent source of whole gains" to be confusing and that the FDA has been working on developing a better definition of the term for some time now. The FDA has worked out a new system of classification based on the number of grams of whole grains in a food and has eliminated any good/excellent designations. The new labels are an eye-catching black and gold and clearly state the number of grams of whole grains per serving, as well as the recommended daily amount of 48grams, as suggested by MyPyramid. This eliminates any guess work - though it does call for a little bit of math - on the part of the consumer.
Products must be authorized to use the stamp, getting approval from the FDA or the UDSA, depending on what type of food the item is, since the two groups regulate different commodities. The USDA covers meat, dairy and eggs and the stamp is approved for use on those products, as well as the grains and other foods that the FDA regulates, if they contain whole grains.
So far, more than 800 products are approved. You can see a full list here or, of course, keep an eye out for the labels while you shop.