There are many "moments" in music that can be considered magical.  But if
you get down to a magical "note" or two, I must say these:

1) The chords accompanying Desdemona saying farewell to Emilia and her high
A-flat note after that in Act IV, Verdi's Otello.

2) The end of 1st movement development, Schubert's Sonata #21.

--Tim Hu