Grove Music Online
Grove Music Online contains the New Grove Dictionary of Opera, FYI - the fabulous appendices from the back of the print vol. 4 (for role names and aria/ensemble titles) will be found under the TOOLS & RESOURCES link. Consult Grove to find articles on composers, singers, teachers, and genres (opera, art song, vocalise, etc.). Composers' articles contain WORKS LISTS - handy for verifying titles of songs, first performances, and ORIGINAL KEYS.