Video: Gear > mobs, starring a witch doctor and a barbarian
Below we have the witch doctor going one-on-one (excluding his demonic entourage) with the Bucher and killing him in nine seconds.
According to a member of the incgamers forums, the build this doctor uses is this one. Of course, you'd need some gear first but at least you have some basic strategy of how to kill the fatty.
The next one comes from Kripparrian, currently one of the most popular Diablo 3 streamers. Krip uses one of the standard barbarian late-game builds to do this:
How he survives? With 800 in all resists, 8K armor and 30% block chance.