I've never seen a better low post defender than Sheed in all my years of watching NBA basketball.
Woah... settle down there. Having said that, it's not crazy to think he's one of the best in the NBA currently. The Celtics have faced off against 2 different but great post threats:
Gasol - arguably the best finesse post player in the game.
Howard - lacking skills but has elite power and athleticism.
In both cases, Sheed has done very well against them and has shown an ability to frustrate them both. That at least makes him worth discussing. My votes against Sheed would be he's probably not in good enough shape to play the same quality D for 35 minutes a game. He also has a tendency to pick up a lot of fouls (not even getting into technicals).
As far as who the best in the game is, I'd have to go with Dwight. Help D is his specialty, but there's a reason Perk and KG had little offense against Orlando. For other contenders, I'd throw Perk in there. After him, I'm having a hard time thinking of others. Maybe Duncan, but he's getting older. Bynum definitely has the potential to be. Camby and Noah could also be in the discussion. Anybody else I'm missing?