Christmas carols: Puer natus in Bethlehem
Puer natus in Bethlehem ("A boy is born in Bethlehem") has been around since at least the 13th century. It has been arranged by many composers, including Michael Praetorius, J.S. Bach, and Dieterich Buxtehude.
The first arrangement is by Praetorius, the second by Bach, and the third is a modern arrangement by an unknown composer. (I usually stick to traditional melodies for these posts, but I thought this arrangement was nice, so I'm including it.)
Christ Church Bronxville, 2007:
St. Mark's Youth Choir, 2007(?):