St. Lucy (or St. Lucia), whose feast day is celebrated December 13th, is a shining example of this faith-based unity. She is regarded as a saint not only in the Catholic Church, but also in the Anglican, Lutheran and Orthodox Churches.
While this information is available today at the click of a mouse, I discovered this before the days of Wikipedia.
My family is a mini-United Nations and I have a Swedish uncle who was Lutheran until a few years ago. While I knew about St. Lucia from my Italian family, I celebrated the feast day with my Swedish cousins (who are from the Argentine half of my family). My aunt would make traditional Swedish St. Lucia buns -- something between savoury and sweet with saffron in the dough. My Swedish cousins would dust off their Swedish language skills and sing "Santa Lucia" ... which I knew in Italian. The one cousin who was a whole year-and-a-half older than us would always try to wear the traditional wreath adorned with candles. She never actually got to light the candles as she walked around singing and handing out the St. Lucia buns to the family.
What we never realized as children, because these things don't occur to children, is that we were having an ecumenical moment, celebrating a rare feast day shared between these Christian churches. Looking back today, I see in that mixed family celebration of St. Lucy the Communion of Saints in action.
Photo credit: Holger Ellgaard