This is for free players and for members who do not wish to spend $99.95 for 40k AC's and an IDoA:

As soon as possible, kill Diabolical Warlord for Burning Blade.

At level 80, do the Celestial Arena for Burning Blade of Abezeth.

This is for all players:

At level 85 - 90, start grinding the Necrotic Sword of Doom.

Obtain at least the following classes:  Legion Revenant, Stonecrusher, ArchPaladin, and Lord of Order.  Preferably Void Highlord as well.

Obtain the Head of the Legion Beast and / or the Ascended Omni Cowl.

Do Ultra Boss fights, especially Champion Drakath and Ultra Avatar Tyndarius, for their items. although make sure you come prepared!  If for nothing else, you wish to pick up Infernal Flame Pyromancer from Ultra Avatar Tyndarius!