Thunderfury was nice, but...
I am piggybacking this based on Tengenstein's statement in this thread.
Prot warriors had an awesome legendary in Vanilla, and many warriors used it up to first kills in Black Temple (seen videos of kungen using it on firsts).
Either way, I think we shield tanks are way overdue for a legendary. In Naxx, Atiesh was given to all staff classes. In BC, DW DPS warriors/rogues got the Glaives, and hunters had a bow from Sunwell. In Wrath, healers had a hammer from Ulduar and tank DKs and DPS 2h classes had Shadowmourne. In Cataclysm, we have a DPS caster staff and now Rogue-only Fangs of the Father (rogues could use Tfury, Glaives before this as well).
It's high time for either: a 1h tank weapon, or a really ultra-badass shield.