I don't generally enjoy Mozart, but his Requiem is incredible.

"Salvation is Created" is a choral piece by Pavel Tchesnokov, mindblowingly beautiful, especially with a good section of deep Russian basses.

Many Renaissance masses and motets also, Josquin and Palestrina especially.

I am almost grateful these aren't usually performed in services--I won't speak of Bach, since it is almost worth pretending to have found faith just to sing in the church choir.