Threadless 1⅛" FSA headset. Seems to be about £50 in a lot of places but On One are selling their last 20 for way about 15 quid.
http://www.on-one.co.uk/i/q/HSFSOX/fsa-orbit-x-headset
http://www.on-one.co.uk/i/q/HSFSOX/fsa-orbit-x-headset
