Legendary weapons are a status symbol. They show the dedication and skill of a player and his or her guild. However, not all legendary weapons are equal, and not all are usable by every class. In vanilla WoW, we had a 2H mace, a 1H tanking sword, and a caster staff. In The Burning Crusade, we had the Warglaives (DPS swords) and Thori'dal (bow). In Wrath, we had Val'anyr (1H healer mace) and Shadowmourne (2H axe.) Now in Cataclysm, we are getting another caster staff, and who knows what else is on the horizon.
I am glad Blizzard brought back the epic quest chain requirements for Dragonwrath, as I was severely disappointed in how Thori'dal and Warglaives were obtained. Personally, I think we need a legendary shield, one that, similar to Atiesh, you pick which version you want at the end of the chain, so that it could be a tank or healer shield. I would also like to see a legendary fishing po -- okay, sorry, I couldn't say that with a straight face. As for the legendary shield, let it be forged from some of Deathwing's scales or something similar that seems Cata-appropriate; in lore, Deathwing's forged scales are extremely tough, so it could easily fit into the lore and be made into a grand, epic quest chain.
What legendary would you like to see next -- and if you are feeling extra imaginative, how should one go about acquiring it?