TOD:
Way too many to list, but a few:
Benjamin Britten: War Requiem, the composer conducting
Herbert Howells: Requiem (a cappella) and the Hymnus Paradisi (with orchestra), which share musical material
Maurice Durufle: Requiem - the Robert Shaw recording with orchestra is excellent, but I also like the version with just organ and a few strings
William Walton: Belshazzar's Feast, as DR elmore3003 mentioned. The Robert Shaw recording is very good.
All of the J.S. Bach masterpieces: the St. John and the St. Matthew Passions, the Mass in B minor, the Christmas Oratorio
Vaughan Williams: Mass in G minor
Igor Stravinsky: Mass
Leonard Bernstein: Mass