As much as I dislike the guy, as someone else mentioned, Deon Sanders was a great cover corner. And he would get the picks and bring 'em back the other way for TDs just like Reed does. He also returned kicks and took his share of them to the house too. Couldn't tackle worth a lick but he could cover and had that magic with the ball when he got his hands on it.
Lawrence Taylor has to be in the conversation as does Reggie White. Let's not forget Eller and Paige, the stalwarts of argueably the best D line ever assembled, the Purple People Eaters.
But the guy who gets my vote as the best defensive player of all time was the guy who led the best defense I ever saw, the guy who is now the head coach of the FortyNiners, Mike Singletary. That guy was a bugeyed beast at middle linebacker and set the tone for the most smothering defense that ever took the field, the '85 Bears.