I've completed normal and I'm working my way through nightmare, all the while keeping my eye on the AH for gear with:
+life on hit/life % of damage
My planned build would be: http://us.battle.net/d3/en/calculator/barbarian#WXYVkg!cdb!ccZcbZ
For those who have reached late hell/inferno, do you think this build would be viable? In my own thoughts, I've decided that if I'm within melee range of a few mobs, my lifesteal will be enough to keep me alive but if I'm surrounded or getting attacked from range, I'll be pretty screwed.