Well, the first that comes to mind is the silk headdress from Coppergate that I just read about a couple of days ago. Now of course I'm having trouble finding that source right now... but it's the cap that is being discussed here: http://docs7.chomikuj.pl/116468363,0,0,NORSE_WOMANS_LINEN_HEAD-DRESS.pdf
I'll be back for more links! Good luck! =)
I dont´t know of any published headwear, but there is the fragment of a straw-hat from Lengberg and a makeshift linen bonnet (15th century). They are briefly mentioned here: http://www.uibk.ac.at/urgeschichte/projekte_forschung/textilien-lengberg/forschungsprojekt-ma-textilien-lengberg.html.
There are cap-like hats from the Netherlands photographed with huge photos (and references to other articles about them) in:
Brandenburgh, C.R. 2010. Early medieval textile remains from settlements in the Netherlands. An evaluation of textile production. Journal of Archaeology in the Low Countries 2(1); 41-79.
http://dpc.uba.uva.nl/jalc/02/nr01/a02
(It includes a cap from Dokkum that is similar to the cap from York that Fanny mentioned.)
Narrower caps are also in:
Heckett, Elizabeth. 2003. "Viking Age Headcoverings from Dublin." Dublin: Royal Irish Academy.
I'm sure I'll press 'hit comment' and remember some more.
sorry, 'post comment', not 'hit comment'.
Also, a blue felt hat from England:
http://www.concealedgarments.org/cache/28593/
This hat from Novgorod: http://www.booksite.ru/enciklopedia/clothes/3.htm
And http://www.imareal.oeaw.ac.at/realonline/ has a straw hat from Kempten (Bild: 016174)
In 'Textiles and Clothing 1150-1450' (the museum of London book) there's a lump of fabric tentatively identified as one of these sort of hats: http://t2.gstatic.com/images?q=tbn:ANd9GcTsXfvVcsLrwBO1o39fkF-AP9oGJZwgNawg1cw3GWRWQ4YE7leZ
Thanks again, everybody!
fiofiorina, yes, I would love to have the reference.
paantha, wow - I have the book, and I am using it regularly, but that had somehow really slipped my attention.
Iðunn, thanks for the offer! I think that Icelandic sagas may be a bit much for the project, though, since I'm trying to base it on the actual extant pieces as much as possible...
Just read some info on the so called Orkney Hood - a marvellous garment... I have never seen anything like it! http://www.archaeologyonline.org/Documents/TheOrkneyHood.pdf