These are the standard starting places for research or reference.
Baker's Biographical Dictionary of Musicians, Centennial ed. 6 vols. Nicolas Slonimsky, ed. emeritus. New York: Schirmer Books, 2001.
Musicmedia Reference ML105 .B16 2001
Recognized as the standard biographical dictionary in English, Baker's covers groups as well as individuals. Articles are usually more concise than those in Grove's. Note the indexes by nationality and genre (by historical period for people in art music) and the index listing women composers and musicians.
Online version (partial coverage): Gale Biography in Context—contains most of the articles but inexplicably lacks some important ones. Also lacks the bibliographies and work-lists that are part of the biographies in the print version.