One of my favorite videos is this 1977 Austrian concert... My favorite carol is probably: (At 18:27)
O du fröhliche, o du selige, (O you joyful, O you blessed,)
Gnadenbringende Weihnachtszeit! (Grace-bringing Christmas time!)
1. Welt ging verloren, Christ ist geboren. (The world was lost, Christ is born.)
2. Christ ist erschienen, uns zu versühnen. (Christ appeared to our atonement.)
3. Himmlische Heere, jauchzen dir Ehre. (Heavenly hosts rejoicing to honor you.)
Freue, freue dich, o Christenheit. (Rejoice, rejoice, O Christendom!)
Very easy to remember!
And for carols in English:
Of those, "Hark, the Herald Angels Sing" is probably my favorite.