"Dig into dance history by seeing correspondance by George Balanchine or photos of ballerinas at New York City Ballet. Look at a Labanotation of Serenade at the Dance Notation Bureau. Or listen to an interview with Martha Graham at the Jerome Robbins Dance Division Oral History Archive and Project at the New York Public Library for the Performing Arts."
I have visited the Performing Arts Library (conveniently located at Lincoln Center); they have a wonderful search function where you can type in the name of your favourite dancer and see a list of all the videos that they're on in the library's holdings, and then go and watch the videos. Some of these are recordings that are not pubicly available; for instance I saw a video of Robert Tewsley and the Stuttgart Ballet in Glen Tetley's Rite of Spring. You will need a NY Public Library library card, but visitors from outside NY can easily get a temporary one (good for three days) at the front desk.
Another good source for dance in NY is the
The Paley Center for Media (formerly the Museum of Television & Radio), where as I recall you can watch videos of dance performances that have been broadcast (e.g. Dance in America).
25 West 52 Street
New York, NY 10019
Closed: Mondays & Tuesdays
Children under 14 $5