Vigilance is a warrior talent available at level 75.
Tips and Tactics
Vigilance is best put on either the healer or a DPS class which produces the most threat. It helps to have Omen (or a similar threat-tracking addon) or, if the party members don't have Omen, a damage meter addon so you can determine which party or raid member is producing the most threat. This will make it so that they lose a good chunk of the threat they cause, and you gain whatever they lose. The lack of a cooldown on Taunt is useful as well, as it allows you to immediately take the mob off of the party/raid member should you lose aggro, even if you've already used Taunt in the past 6 seconds.
Patch changes
Patch 5.3.0 (20-May-2013): Vigilance now resets the cooldown on Taunt in addition to its current effects.
Patch 4.0.6 (8-Feb-2011): The wording in the tooltip for Vigilance was inconsistent with other abilities and has been updated.
Patch 3.3.0 (08-Dec-2009): The threat transfer granted by this ability will now reactivate when Tricks of the Trade or Misdirection cast by the Vigilance target expires.
Patch 3.2.0 (04-Aug-2009): This talent and Blessing of Sanctuary will now both be able to be cast on the same target without sometimes overwriting each other.