Five things to consider when researching with the Internet (aka The CRAAP Test!) ~
If you cannot answer these questions satisfactorily, reconsider using the information as a source.
Dance
Ballerina Gallery - Ballerina photo gallery
Dance Heritage Collection - dance collection to preserve America's dance
Society of Dance History Scholars - Research, history, publications
Costume
Costume Page - Costume images and history
Costumer's Manifesto - Great resource for costume history by period
Stage Craft
TheatreCrafts - Useful links and practical information for all aspects of technical stagecraft, including an online glossary and links to effects, sound, lighting, props, and stage management
Theatron - 3D models of various stages
Theatre
Cesar - Database contains information on all aspects of the French theatre between 1600 and 1800
Didaskalia - An electronic journal and resource dedicated to the study of ancient Greek and Roman drama in performance
Internet Broadway Database - The IBDB (Internet Broadway Database) archive is the official database for Broadway theatre information. IBDB provides records of productions from the beginnings of New York theatre until today.
Living PlayBook - Hundreds of Acting games
Lortel Archives - Off-Broadway Database provides a catalogue of shows produced Off-Broadway.
Noh Plays - English translations of 13 Japanese Noh plays, including a glossary
Performing Arts Encyclopedia - Explore music, theater, and dance at the Library of Congress
Speech Accent Archive - Audio samples of various language backgrounds
Theatre History on the Web - Jack Wolcott's website of theatre history resources
Virtual Library of Theatre and Drama - resources from more than 50 countries around the world