Dramatists Play Service: Playfinder, allows searching by author, title, keyword, or gender, and number of cast members. Can purchase books or browse the catalog.
Inter-Play: an Online Index to Plays in Collections, Anthologies and Periodicals.
Ottemiller, John H. Index to Plays in Collections Ottemiller’s Index to Plays in Collections : an author and title index to plays appearing in collections published between 1900 and 1985. Metuchen, H.J.: Scarecrow Press, 1988.
Samuel French: Theatre and plays bookshop.