Howard
Bogut
Ilgauskas
Horford
Perkins
Okafor
I think there's a pretty big gap between 1 and 2, and then between 3 and 4. Bogut and Ilgauskas are about equal to me, I'll take Bogut because he's much younger and still getting better. Horford and Perkins are really close too, but I think Horford's advantage in offense outweighs Perk's advantage in defense. I already think Perkins is a little better than Okafor.
I don't consider Sheed a center, and Jermaine O'Neal needs to stay healthy before I'll give him a look on this list. Dalembert would have been around 5 on this list before this year.