O Holy Night by Adolphe Adam is arranged here by Peter Covino, Jr., for solo voice or duet, or for unison choir or 2 part choir, and piano. This arrangement modulates everywhere. Order by mail here for $2.50 each. Free LDS choir sheet music, hymn arrangements, and piano and voice songs are available here.
It is also available for full orchestra and other combinations at this site. You can request a key.