Robert Baldwin lists some quintessential late works and asks:

>Any other candidates you'd recommend?

Here are a few:

   Mahler: Ninth Symphony
            Adagio from 10th Symphony
            Das Lied von der Erde
   Mozart: Divertimento for String Trio, K563
            The last  viola quintet- I forget k number.
   Janacek: Galgolitic Mass
   Strauss: Oboe Concerto
            Metamorphosis
   Haydn: The Creation
   Verdi: Four Sacred Pieces

Professor Bernard Chasan
Physics Department, Boston University