Does anyone have any ideas on a headpiece that I can use for a custom Tulak Hord? I was thinking of using the Imperial Combat driver helmet. 

I would use the Old Republic Sith Trooper helmet, if you have any on hand.

I would say probably this one > http://brickset.com/parts/4226000

with maybe a custom darth nihilus underneath?

Good shout Krask - I think that would be a good combo to go with.

Found a custom one on Flickr:

But I think the Dark Knight helmet works best