Hey currently im in act 3 nightmare right now and found a build that quite funny and does alot of damage. What happens is that im able to lifesteal because of "relentless" and bloodthirst and rend+bloodlust keep me up. Just like to hear your thoughts and you should try it out.
http://us.battle.net/d3/en/calculator/barbarian#WcSkiP!Ude!aZZbaZ