There are even some pieces for choir and guitar--one by Castelnuovo-Tedesco as I recall. In any case, here is a touching piece for choir, a cover of a song by Tears for Fears. The idea of having the performers disappear bit by bit originated with Joseph Haydn in his "Farewell" Symphony. This is the Wuppertal Boys Choir from Germany:
Another wonderful choir video came from a few years ago when a Canadian choir suddenly appeared in a shopping mall. This one is worth putting up again:
You see, it works both ways, from many to one or from one to many.
While we are doing choral music, let's end with a piece by a composer who really is like none other. Arvo Pärt was born in Estonia in 1935 and writes music that seems truly timeless. Steve Reich commented once that "His music fulfills a deep human need that has nothing to do with fashion". Here is a piece for mixed choir from 1989: Magnificat.