1 Barb / 1 Monk / 2 Wizards.

1 button!

I doubt this build will work right out the box at level 1, you need to be 60 and have a few gold to gear the wizards with 35% crit chance and 20~ arcane power on crit. But when it does work, it's glorious and smooth. Did I mention you only have to press 1 button the entire time?

Barb - 20% all resist and 20% armor buff for group
http://us.battle.net/d3/en/calculato...kPc!ZhY!YYZcZZ

Monk - 24%(48% almost always uptime) group damage buff / additional 16% group damage buff 100% uptime / 10% group damage buff 100% uptime with 30% snare and 20% attack speed reduce on enemies totaling 74% group damage buff up 3/4th of the time and 50% any other time.... massive.
http://us.battle.net/d3/en/calculato...fkg!fbU!ccbZab

Wizard 1 - 20% group damage buff from Slow time, 15% group damage buff from Frost Nova - 35% group damage buff - 100% uptime
http://us.battle.net/d3/en/calculato...hYX!WXg!YcZcca

Wizard 2 - 10% group attack speed buff - 100% uptime
http://us.battle.net/d3/en/calculato...hYX!WXg!YcccZa

How to make it all 1 button? I'll give my keybindings, make it your own

Main attack left click is Bash / Crippling Wave/ Energy Twister. Holding shift and left click during combat is given. Just keep them pressed down.
Right click is for 2 minute buffs, so only needed once every 2 minutes! Which is Battle Rage / Storm Armor (can be swapped with Force armor if survivability issues) / Earth Ally.

I use Barb as the main.
My main key I press is Q again you can put these to anything.
I have Warcry set to the O key. In ISboxer set up a keymap with 2 steps. First step Action O to Character 1. Check off do not advance to the next step for at least 50.0 seconds and only trigger once. The entire top bar should be checked. Copy the first step and paste it in again, so both steps are identical. Set the main hotkey button to Q. Right click the hotkey button and select create alternate hotkey, for this hotkey have it trigger as shift + Q. This will make it so when you press it with or without the shift key it always triggers. Do this for every hotkey.

I have Slow time set to "L".
Breath of Heaven, Frost Nova, Hammer of the Ancients set to "Q"
Chain Reaction Set to "M"
Diamond Skin set to "P"

Make a new keymap. First step L -> all. Second step Q / M / P -> all, should all be in the same step. At the top select Do not advance to the next step for at least 8.0 seconds.
What this keymap does is hits Slow time every 8 seconds (which is the duration for slow time) and then always spams the rest of the abilities. By spamming Breath of Heaven (cooldown is 15 seconds) it gives you 100% uptime on the 16% group damage buff which lasts for 15 seconds.
It also spams the Hammer of the ancients ability for the Barb, and makes the Wizards CM/WW build work but hitting their 3 main keys whenever they are up.
Make sure to set this hotkey to Q and create an alternate to shift Q

I have Mantra of Conviction and Rend on the "R" hotkey.
Make a new keymap. 1 step R->all, Do not advance to the next step for at least 5 seconds and only trigger once. Copy and paste the same step. It appears to work if you only have it as one step but just to be sure, make it two.
This will give you Mantra of Conviction up 3 out of every 5 seconds, and have you rend every 5 seconds which is the duration of it. If you notice you have spirit generation issues keeping it up this often, break it off into two seperate hotkeys and modify the occurrence accordingly.
Make sure to set this hotkey to Q and create an alternate to shift Q

That's it for spamming the one button, simply hold shift / left click in combat and mash that Q key. I'll try to get a video of it in action to show the simplicity of it.

For additional keys. I have Cyclone strike bound to Mouse 4. Which sucks in all the targets on top of you. Works well because they are already frozen and this makes it so you can concentrate the Energy Twisters on you and not have to spread them out.
Wrath of the Berserker which isn't really even needed just a nice DPS boost is bound to Shift / D for me for whatever reason, using it on bosses and critting for 2.4 million at only 112k unbuffed dps is always nice. Watch out for that damage reflect though! haha.
Serenity is bound to the W key which is a 1 second group invulnerability every 20 seconds. This is nice if you don't want to move out of frozen (just time it right) or as an oh crap card.

Also make sure you bind a movement key, I use space - this helps you run around without worrying about attacking things due to left clicking.

The overall feel of this build is .. everything is frozen. I do uber siegebreaker / zoltun at mp5 with no issues and they stay perma frozen the entire fight. Same goes for the other uber battles except madgha, she likes to go invuln. The Slow time bubbles do help to dodge her attacks though.
Right now I don't go any higher than MP5 because it frankly just isn't efficient, you can go higher with this build as the fights consist of everything frozen and locked down, it's just a matter of how much dps you have.

Hope you enjoy!