I'm a sucker for the Old Traditional ones. The older and more traditional they are, the more I love them. Veni Veni Emmanuel
(This carol dates back to the 8th Century.) Ave Maria by Franz Biebl as sung by Chanticleer
What I love about this particular arrangement is that the interspersing verses actually tell the story of the Annunciation. Also it splits the choir in two with SATB and SATB layering over each other. Stille Nacht as sung by the Vienna Boys Choir
I also love choirs. I think choirs are especially wonderful for religious music, as they are not there to promote one individual's ego, but rather to lead the congregation in praising the Lord.