Web site about plaids: http://tartanweb.com/intro.htm
A practical guide to the draped clothes native to Britain: http://www.simon-s.net/clothes/
Simon Chadwick's very informative page on how ancient celts draped themselves.
Roman Clothing I: Introduction, undergarments, men's clothing : tunic and toga: http://www.vroma.org/~bmcmanus/clothing.html
Roman Clothing II: Women's clothes: peplos,chiton, stola. Hairstyles and jewelry: http://www.vroma.org/~bmcmanus/clothing2.html
Roman Clothing Sources: Books and links related to Roman clothing: http://www.vroma.org/~bmcmanus/clothing_sources.html
Middle-Eastern clothing through the ages, including draped clothes and headdresses from Roman times (be patient and scroll to the end... somewhat scholarly...):
How did Greek and Roman Goddesses drape their divine bodies? See the answer given by an exhibition at the Metropolitan Museum of Art: