What gear is the most in demand for PVP?

Echoing Fury (Crit Damage %, and Has Socket) is my favorite item to flip at the moment, and occasionally I sell rare shields (200+ Vitality, Life %, All Resist, 150+ Dexterity...).

I'd like to expand on the PVP theme, however, and look for stuff that is necessary to have in order to have decent dueling power.