Seriously, I'd have Brock at the top of that list.
Not only does his face look scary, but his body is as intimidating as it gets. When he flexes his trapezius it looks like you'll need a shotgun to knock him out; which may be true since brock has took some hard punches but has never been KO'd.
I remember seeing him in MMA for the first time against Mir, I thought 'Man, Mir has got to be shitting bricks right now'. My thoughts were echo'd by Mir who later admittted that he was 'very impressed' by Brocks physique.
You know that when a guy is multi-millionaire but still chooses to live a basic life, so he doesn't lose his edge, is a force to be reckoned with. I hate hunting for no reason; but hunting and killing your food is to be respected - as is Brock.