So, let's go.
I have an idea about legendaries for each class cuz it is possible to have a leg. weapon with effects in 4.3.4.
If you're prot warrior or paladin - Thunderfury (MH)
If you're blood dk - Shadowmourne
If you're a feral - (???)
Arms war - shadowmourne
Fury war - two shadowmournes or two thunderfuries
Retribution pala - shadowmourne
unholy dk - shadowmourne
frost dk - (???)
rogues: sub/assasin - fangs, combat - azzinoth
mage, warlock, balance druid, shadow priest, elemental shaman - dragonwrath
all healers - val'anyr
hunters - bow from sunwell
enhancement shaman - (???)
How to get it: questlines in 1-man raid dungeons.
P.S Weapons will be upgraded with "IceCold Upgrader", of course)