Seems like a few people don't realize just how great Ted Williams really was. His OPS over his CAREER was over 1.100. To put that in perspective, only two players have hit that mark in any given season over the last decade (Pujols in three years, Bonds in five if I recall correctly). Again: Williams did this over his entire career.
Pedro was an excellent pitcher. Clemens was an excellent pitcher. But you could make a very compelling argument that Ted Williams was the best hitter of all-time - and he missed four of his prime years when he was serving in the army. Neither Martinez nor Clemens can make that claim.
In my opinion, Ted Williams and Bill Russell can't be left off. I can't really comment on Bobby Orr because I don't know hockey very well (feel free to educate me on Orr). Brady would be battling Auerbach and Bird for the last spot. I honestly feel that Auerbach and Bird meant more to the sport of basketball than Brady does to football, but I might put Brady on just to have a rep from each of the four major sports.
Just my two cents. Good topic, TP to the topic creator.