Barbarians, clearly feeling neglected in the wake of the Invulnerable Wizard exploit, have discovered a means to become semi-invulnerable themselves. It's not quite as powerful an exploit, as it simply makes permanent the effects of Furious Charge with Dreadnought Rune. That is: almost doubled weapon damage and 8% life regeneration each time you land a hit. For most barbarians, that's as good as invincible, and this exploit hasn't yet been hotfixed by Blizzard. There's a video of the trick in action below.
The exploit is triggered by charging into the cutscene immediately before a boss, which for whatever reason causes the game to forget to remove the buffs of the charge skill. Here's a guy using the exploit to easily take down Ghom.
The thread on the Diablo 3 forum details the exact steps required. Seems Blizzard's plea to report all hacks and exploits to them, rather than to YouTube, has gone unheeded.