AFL-CIO Labor History: Triangle Shirtwaist Fire
Cornell University: Remembering the Fire Research Site (tons of info! explore the whole site!)
Cornell University: Sweatshops & Strikes Before 1911
PBS Learning Media Video: Triangle Factory Strike
Smithsonian: Uncovering the Triangle Shirtwaist Factory Fire
Cornell University: TSFD Primary Sources Primary Sources!
Digital Public Library of America: Children in Progressive-Era America (big overview of the time period, plus source pics)
Google Arts & Culture: Triangle Shirtwaist Factory Fire
Library of Congress Chronicling America: TSFD Newspaper Articles Primary Sources!