Contains signed articles on people, places, genres, instruments, etc. Most composer articles have works lists, which serve as indexes to that composer's Collected Works; extensive bibliographies (organized from oldest to newest).
The New Grove II is the major English-language scholarly resource for information about music, theory, instruments, musical genres, librettists, composers and performers.
The German-language equivalent of the New Grove Dictionary; even if you do not read German, composers' dates, and bibliographies are very easy to navigate and interpret.
The New Grove Dictionary of Music and Musicians by 
Musik in Geschichte und Gegenwart by 
