I found that nothing really looks right when worn with Ancient Falmer Armour. Its so different to everything else.
I suppose you could try an elven helmet? I know its a completely different colour and stuff, but the armour sets as a whole look sort of similar.
I wore a novice mage hood for a bit and that looked ok, and you can get an unenchanted version ( if you like enchanting ), it's not a helmet, but may be preferable to a circlet. Unless you aren't too bothered how it looks, and just want something that will stop damage, in which case Dragonscale. If you can smith it.
It's wierd how you cant get the actual Ancient Falmer Helmet in-game, they designed it and everything, I believe you can get it on PC with console commands.