Baker's Biographical Dictionary of Musicians. The highly respected Baker's covers groups as well as individuals. Of special interest are the indexes by nationality and genre (actually by historical period for people in art music) and the index listing women composers and musicians. Gale Biography in Context supplies some of the content, but omits the bibliographies and works lists from the print version's articles, and inexplicably lacks some articles entirely.
MUSICMEDIA REFERENCE ML105 .B16 2001