The titles that are already suggested are great. One other very nice “every year” piece that I can recommend is:
The Irish Blessing
Joyce Eilers-Bacak – Hal Leonard Corporation
Using the traditional lyric, May the Road Rise Up to Meet You, Joyce’s SATB a cappella composition makes an outstanding concert closer. The voice parts are placed within moderate ranges with conservative voice leading and a very strong closing statement.
When I was a high school teacher this was our song to sing at graduation, and it was always quite lovely and fun to sing even after many years. It’s been around a while, but I still like it. Be Well, Chris Peterson