Diplomatic Papers Clicky
This is one of the best tank clickies you can get in the game and it works as basically a ghetto Pain Doesn't Hurt/No Time to Bleed clicky. Of course other classes aside from tanks benefit from this item as well - irf you're a class that takes hits at all or someone who likes to solo you'll get a ton of use out of this item.
Diplomatic Immunity is the buff that it casts on your character. It lasts for about 40 seconds and absorbs 5000 damage a hit up to a total of 50,000 damage. It absorbs both melee and spell damage which increases how awesome it is significantly.
Out of all the Anniversary clickies this one as well as the Miniature Horn of Unity are the ones you will want to get first.