not in any order - foreman, tyson, frazier, ali, liston, lewis, luis, marciano, holyfield, jack johnson, john l sullivan.
i chose these of the top of my head just cos they are the heavies that spring to mind as having the most significance and impact on the sport. would also make for some awesome fights. i know style wise it might be a blow out for someone like foreman fight john l sullivan. but i had to put him in cos he was the first heavy weight champ and from what i've read and seen was hard as nails.