Fellside has a woderful sampler of various groups doing unaccompanied singing--it's called Voices in Harmony. Even better, it's a 2-CD set for the price of one. $13.98 at CAMSCO (who also carries Coope, Boyes and Simpson, Cockersdale, The Copper Family, The Johnson Girls, The Boarding Party and all the other marvelous acapella groups.)