Also the traditional barbershop quartet for acapella. Interestingly, I like the 5-piece versions of all 3 of these: add a keyboardist to the rock band, a piano

Also the traditional barbershop quartet for acapella. Interestingly, I like the 5-piece versions of all 3 of these: add a keyboardist to the rock band, a piano or harpsichord to the classical string or woodwind quartet, a female vocalist to the acapella group. Having two leads lets you do much more intricate countermelodies and harmonies.