The first one that came to my mind was Denzel as Malcom X. Was amazing.
And I think there are people that won't ever be portrayed to anyone's satisfaction. For example I think Will Smith did a great job in Ali, but Mohamed Ali is just a character that I don't think anyone will ever be able to capture. You'd think that the closest person to him as far as his charisma would be WIll, but he still fell far short of capturing it completely.
Jim Carey as Andy Kaufman in "Man On The Moon". Not a Carey fan, but I was a huge Andy fan. The portrayal is uncanny.
I'm betting Borat as Freddie Mercury in the upcoming bio pic will be stellar. He's a shape shifter.
I got really excited when I heard that Cohen was going to be Freddie Mercury. I'm really interested to see him devote himself to something serious instead of the silly stuff he's done in Ali G and the other comedy movies.... plus we all know he can handle the stache.