Musicals 101
Musicals 101: History of the Musical Stage: Ziegfeld Follies
This article gives a history of the Ziegfeld Follies, with information on its creator Florenz Ziegfield, its origin, and the performers. The site also includes thumbnails of pictures of the Follies.
Duke University
Historical American Sheet Music: Mandy by Irving Berlin
Take a look at the sheet music from Irving Berlin's "Mandy", performed at Ziegfeld Follies in 1919. Very cool old poster.