6. Jack Johnson: at ~6'1 and 208lbs he would be small by today's standards but was so fast and skilled that I don't see his lack of size hurting him too bad, or at all actually. Great fighter but since fighters back then basically sucked he had pretty weak opposition. He reminds me a lot of a bigger, stronger and faster version of Jersey Joe Walcott who gave an aged Joe Louis fits and had Rocky Marciano beat until getting clobbered by a huge right in the 13th round (which was the same round that Louis caught him in as well, 13 was definately an unlucky number for Jersey Joe).
7. Lennox Lewis: 6'5 240lbs. Big and very strong with crushing power in his right hand. Didn't really get the respect he was due until the Holyfield fights and the Holyfield he beat was past his prime but Lewis is still an all time great fighter. Great longevity at the top.
8. Sonny Liston: 6'0 1/2 212lbs. Big, scary, huge fists, long reach and a great jab, this guy absolutely cleaned out the division in the late 50's early 60's and punctuated his run with two crushing 1st round kayo's of Floyd Patterson.
9. Jack Dempsey: 6'1 187lbs. I really didn't want to put a guy this small and with such shitty comp on the list but I don't think this is a ridiculous rank for him. He had the ability to fight in a lot of different styles and beat some good big guys in Jess Willard and Angel Firpo in addition to absolutely destroying every white fighter in the division on his way up.
10. Joe Frazier: 5'11 205lbs. It's the loss to Foreman that really hurts his legacy but his other accomplishments are so great that he needs to be on this list. Foreman was a terrible match up for him. The other guys on this list could have all found a way to beat Foreman (I'm not saying they would, but it's possible), but if Frazier fought Foreman 100 times he would get knocked out within the first 3 rounds 100 times. Still a hell of a fighter though.
Rocky (Marciano) does not make this list as a basically view him as a less effective version of Smokin' Joe. I love the Rock, but I don't see him in the top 10.
p.s.: I'm pretty confident in having picked the 10 best heavyweights but I am not confident at all about the order I have put them in.