I make no claim of completeness; I just started compiling this list. If your group isn't here and you want it to be, e-mail me the URL. Most Harvard organizations' websites are listed here, sorted by category; for instance the next link takes you to the arts & performance lists.
The men's, mixed, and women's choruses:
Harvard Glee Club, Collegium Musicum, and Radcliffe Choral Society
The other concert choirs here are the Harvard University Choir, affiliated with the Harvard Memorial Church; The Harvard-Radcliffe Chorus, and an (as far as I know) un-auditioned gospel choir, the Kuumba Singers.
There are also about ten small close-harmony (a.k.a. a cappella or ``Doopsie'') groups, mixed as well as SSAA and TTBB; one of these days I'll put all of their web sites here.
a.k.a. ``Pierian Sodality''(?);
the Mozart Society Orchestra, which actually plays Mozart on occasion,
and two student-run chamber orchestras:
Bach Society Orchestra, a chamber orchestra that occasionally programs music of Bach, and
the Brattle Street Chamber Players, a string ensemble that will like never perform any music by Brattle Street, for lack of a composer by that name (though they might conceivably perform music by Tison Street, or more likely perform on Brattle Street).
The Harvard University Band, which includes the Harvard Wind Ensemble and two Jazz Bands.
(Harvard And Radcliffe Musical Outreach to Neighborhood Youth)
MIHNUET (Music In Hospitals and Nursing homes Using Entertainment as Therapy)
Citystep (An annual dance show for local schoolkids, with music written, directed and performed by Harvard students - the choreography etc. is also directed by our students, but that's beyond the scope of this page)