Oxford Music Online
Formerly Grove Music Online, comprises the full text of The New Grove Dictionary of Music and Musicians 2nd ed., The New Grove Dictionary of Opera, The New Grove Dictionary of Jazz 2nd ed. The Oxford Dictionary of Music, and The Oxford Companion to Music 2nd ed.
Dictionary of musical terms that includes pronunciations (with text and audio examples), cross references to terms in other languages, musical examples, quizzes, and simulations.
Performing Arts Encyclopedia
Guide to musical, theatrical, and dance collections available at the Library of Congress. Includes collections, databases, online presentations, exhibits, and finding aids.