Is anyone aware of a list of corporations that fire men for having long hair?
I think a much SHORTER list would be those corporations which DON'T fire men for having long hair.
If you are an "at will" employee, in most states you can be fired for any reason, or even NO reason. The legal exceptions are those reasons which are race, age, gender, etc. based.
Example: A few years ago there was a lawsuit in West Virginia brought by a nurse who had been fired from Hospital A because of persoanl differences with her superiors. She then went to work for Hospital B, but when her old boss at Hosptial A found out, he/she called the nurse's new supervisor and told him/her she was a troublemaker and should be immediately fired. So the nurse was fired from Hospital B. She sued both hospitals on a variety of legal theories, including tortious interference with a contract. The state supreme court bounced her suit, however, since public policy allows for the termination of "at will" employees for any reason whatsoever other than discrimination based upon Federal definitions (of which hair length is not so defined).
My advice is to first check with your company's human resources dept. for a definitive statement of company policy regarding long hair on men. While I suspect that the overwhelming majority of companies have an official policy of discouraging long hair, there are those few which do permit it as long as it is clean and neat.