Almost a decade after the OP's request, here's one of my favourites for 4 parts a cappella. It's arranged for women; for all male voices transpose down about 4 whole tones; for mixed voices have men sing the lower parts and women singing the higher ones. If you have really high sopranos available, transpose it up a couple of tones and have some of the men double the bass and melody an octave lower (which would make 6 parts total).