The vocal group Manhattan Transfer first formed in 1969 and worked their way to find a sound, with five people involved. By 1972, the line-up had changed to just four, with only one original member surviving, Tim Hauser. Alan Paul, Janis Siegel, and Laurel Massé were brought on board, and the direction of the group moved to a more jazz-driven sound. In 1978, Massé was injured in a car accident, and replaced by Cheryl Bentyne, and that is the line-up that exists today. The acapella/doo-whop/jazz/pop sound propelled them to high placements on the charts from the mid 70s to the early 80s, with songs as varied as Chanson D'Amour, Twilight Zone, and Boy From New York City.
In 1992 they released The Christmas Album, with 11 strong songs done as only they could deliver. Part of the push included an appearance on the Tony Bennett Christmas special on TV, and where they sang The Christmas Song with Tony.
One of my favorite songs they did was Birdland, which is still incredible. They use their voices so well, like additional instruments for the orchestra. Powerful.
You can find out more about Manhattan Transfer on their official website here.