Lombardi, Laundry, Shula, Halas, Walsh, Gibbs and Noll. I am not sure of the order but I know who is in the conversation (Belicheck perhaps once he is done) and Noll was one of the greatest.
Besides great football he instilled great carachter. The steel curtain was the greatest defense of all time. The 85 Bears and 72 Dolphins can be argued had the best defense in a season but the Steelers defense sustained a dominanace over time I have not seen since.
Other then Franco Harris always running out of bounds rather then getting the extra 3 yards the Steelers of the 70's were some of the greatest the NFL has ever seen.