Victoria and Albert Museum - Theatre and Performance - A collection of theatrical designs, memorabilia, books, photographs and specialized archives covers all aspects of the performing arts in the UK, both historically and within the contemporary period.
Victoria and Albert Museum - Fashion - A treasure trove of essays, reading lists, and digital images, spanning centuries.
Costumers Guide to Movie Costumes - A valuable collection of photographs.
Metropolitan Museum of Art - Another resource for images of costumes and historical fashion.
USITT - United States Institute for Theatre Technology - Excellent site for networking and information exchange.
Fashion Encyclopedia - More than 400 biographical entries, alphabetically arranged by designer, as well as entries by country for the Ancient World and Early Cultures, then for European Culture from the 16th through 19th centuries, and The Modern World from 1980-2003.
The Costume Page - Costumer resources online - lots of material here.
The Costumer's Manifesto - This site is mutating into a Wiki, but in the meantime, it offers a broad spectrum of materials, the quality of which varies wildly. Do read the Manifesto itself - for everyone involved in theater production.
Kyoto Costume Institute - A historical dynamic collection of western clothing with respect to social and cultural contexts. Valuable digital archive.
19th Century Actors and Theater Photographs - Over 600 photographs of entertainers and actors who performed on the American stage from the mid to late 19th century.
FARFETCH - A commercial site with fabulous images from more than 400 contemporary international designers. The site also includes news items relating to current trends in the fashion and beauty industries.
Canadian Theatre Encyclopedia - An active online encyclopedia, which collects and disseminates information on contemporary Canadian plays, playwrights and theatrical topics of interest.
Europeana Fashion - A compilation of more than 30 digitized collections of European public and private institutions.