Demon Hunter Nightmare Setup submitted by Prplcheez.
1: Smokescreen (Displacement Rune)
2: Vault (Tumble Rune)
3: Companion (Bat Rune)
4: Elemental Arrow (Ball Lightning)
Left Click: Hungering Arrow (Cinder Arrow)
Right Click: Rapid Fire (Fire Support)
Passives: Tactical Advantage, Vengeance, Night Stalker
Smokescreen and Vault are incredible for avoiding damage. Vault (when not being hindered by server lag) will get you out of range of pretty much anything. Smokescreen is good for dumping aggro off of you and onto your companion/teammates. Tactical Advantage's movespeed boost helps a lot.
The Bat companion's Hatred regen is incredible. With the additional Hatred regen from my crossbows, I can channel Rapid Fire for about 50 seconds straight, if necessary/possible.
Ball Lightning is just insane. It can be fired while on the move, unlike Rapid Fire, has a low Hatred cost, damages virtually infinite enemies at the same time, and will hit larger enemies 2-3 times.
Hungering Arrow isn't used terribly often, though the bouncing effect and the damage over time allows you to be extremely far away from enemies while still dealing damage.
Rapid Fire is extremely dangerous to use, but it seems to be the highest damage skill I have. If I have allies to keep the enemy's attention off of me I can channel it virtually forever. Smokescreen and Vault make it a bit safer, if something runs towards me I can Smokescreen, Vault away, wait for the enemy to attack one of my allies again, then start channeling.
This probably isn't the best build by a long shot, but it's what's been working best for me.
And I'm very much convinced that Elemental Arrow/Ball Lightning is the best Demon Hunter ability by far.