TauntMaster 

TM can be customized to your needs. Click the minimap button or type /tauntmaster or /tm to open the menu.

TauntMaster is a threat-management addon. It automatically displays a button/healthbar for every member of your party or raid.
If the party/raid member begins to gain more threat than the tank, their button turns yellow.
If they begin to insecurely tank, it turns orange.
If they are securely tanking, it turns red.
If another party member gains aggro, simply click their button and TauntMaster will automatically taunt their target off of them.

Pre-Programmed Spells
Taunt Master is pre-programmed to cast the following taunts on whichever party or raid member you click (although in v4.1.0 you can program your own spells and macros):

All Classes:
Ctrl-Click: Assist

Death Knight:
Left Click: Dark Command
Right Click: Death Grip

Druid:
Left Click: Growl
Rigth Click: Challenging Roar

Paladin:
Left Click: Hand of Reckoning
Right Click: Righteous Defense
Ctrl Click: Hand of Protection

Warrior:
Left Click: Taunt
Right Click: Intervene
Shift-Left Click: Challenging Shout

Shortcuts:
/tm - opens up the configuration menu
/tm show - shows tauntmaster
/tm hide - hides tauntmaster
/tm toggle - hides TM if shown, shows TM if hidden
/tm spells - opens up the spell bindings menu
/tm display - opens up the display customization menu
/tm raid - opens up the raid warnings menu

Customizing Spells/Macros:
1. Open up the spell bindings menu to set your own spells and macros to whichever mouse buttons you want.
2. Click which mouse button you'd like to program and enter the exact name of the spell or enter in the macro in the edit box.
3. If you enter a spell name, you MUST select a target
-if you want to cast the spell on a friend (like Righteous Defense or Intervene) then click friend ([@mouseover])
-if you want to cast the spell on an enemy (like taunt, death grip, etc.) click enemy ([@mouseovertarget])
4. Then select the appropriate checkbox for a spell or macro.
5. Finally, press the set button, to save your changes.

Check out http://tauntmaster.com for more information