If I were still directing an active ensemble of musicians and singers, I’d really want to program E’en So, Lord Jesus, Quickly Come.
When I first heard this piece arranged and performed by the Modern Mandolin Quartet, I assumed it was a Renaissance piece. But the American composer Paul Manz is responsible. Like most all great music, it has a timeless quality. Just right for Advent.
Catholic Sensibility 
This has become a standard in the Advent repertoire of many church choirs.
Also, albeit more elliptically, not strictly Advent: Jean Berger’s “The Eyes of All Wait Upon Thee.”
That is lovely; the tune is vaguely similar to “Blest Mary Wanders Through the Thorn” (Maria Durch Ein Dornwald Ging).
Another beautiful one is “Lo, He Comes With Clouds Descending” (to the tune of either Helmsley or Westminster Abbey)
This piece was used yesterday at the local Cathedral during the Offertory at the choir mass. It is very appropiate.