I love the idea of Mozart's Requiem. When I got married a friend sang his Laudate dominum, which is just heart-wrenchingly lovely, so I'd like that again.
And, even though I'm not remotely religious (lapsed left-footer who gave it all up for Lent and never looked back), I love the Sankey hymns, so it would have to be SLEEP ON BELOVED, with all the harmonies...

Sleep on beloved, sleep and take thy rest.
Lay down thy head upon thy Saviour's breast.
We love thee well but Jesus loves thee best;
Goodnight, goodnight, goodnight.

Until our shadows from this earth are cast,
Until He gathers in His sheaves at last,
Until the twilight gloom is overpassed;
Goodnight, goodnight, goodnight.

Until made beautiful by love divine,
Thou in the likeness of thy Lord shall shine,
And He will bring that golden crown of thine;
Goodnight, goodnight, goodnight.

Until we meet again before the throne,
Clothed in the spotless robes he gives his own,
Until we know as we have known;
Goodnight goodnight goodnight.