Looking at the cube powers for general / class specific options it seems like there will be a lot of variation build options rather than sheer power increases. Trading off one power in existing builds for things like In-geom (directly replaces Zodiac ring), Oculus Ring, or Leoric's Crown. Cindercoat, Depth Diggers, Frostburn, Illusory Boots, Nemesis Bracers, Pride's Fall, Stone Gauntlets, Reaper's Wraps. The Furnace for extra elite killing power regardless of build, RoRG in any slot.
Demon Hunters could use Fortress Ballista as a defensive option in non-weapon slot
Wizards could use Aether Walker with any build, that Ray of Frost piercing source may actually be an option, Ashnagarr's Blood Bracer a defensive increase in any slot.
Necromancer jewelry in other slots might produce some interesting combos.