I recently took receipt of a new custom made helmet; a Corinthian Barbute with (re)moveable visor. It is the finest piece in my, slowly, expanding collection. The design is based upon medieval examples, that clearly took their inspiration from the classical world.
The armourer, Milan Marek, has done an excellent job, as I expected from someone with the reputation of being one of the leading European armourers. It is not only a perfect fit but it also has some amazingly graceful lines to it. Seeing a piece like this in the flesh is inspirational for my work. Like holding real chainmail it is an invaluable reference resource.
The articulation on the visor is very smooth, helped by the use of a small disc of leather as a 'washer'. It can also be completely removed. So I guess you get two helmets in one.
I am now looking forward to using it 'in action' at the next roleplaying event. Incidentally it also has a surprisingly good field of vsion through the visor, as the ocular slit is quite close to the eyes.
Milan's work can be found here
I would also recommend browsing the site for armour reference. There is a great range shown, and it is all well photographed and presented.