Just like the title says: a headpiece in the design of the iconic Kaleesh bone masks. I'm a huge fan of Xalek's character design, and this would allow the general appearance of a Kaleesh character without all the hassle of releasing another race. It'd look great on a Sith pureblood or Dathomir Zabrak. It'd look awesome underneath hoods or on it's own, and there are available variations in terms of those little wings on the sides and paint schemes.

Xalek:

http://starwars.wikia.com/wiki/Xivhkalrainik

Kaleesh:

http://img3.wikia.nocookie.net/__cb20120908221812/starwars/images/9/99/Grossh.png