Whats you favorite classical music song?

I'll asume also that you're asking for only songs not pure music , here are my favorites :

1.Lieder : -

*Amy Beach - Ecstasy, Op. 19 No. 2 (Amazing!!)

*Schubert Soprano Lieder :

-Der Musensohn

-Die Forelle D550

-Suleika II Op 31 D 717

-Der Fischer, D225

-Der Wandere an den Mond

*Schubert Male Voice Lieder :

-Abschied schwanengesang D 957-7

-Das Wandern D 795

-Am ersten maimorgen D 344

-An Herrn Josef von Spaun PL,GJ D 749

-Auf der bruck D 853a

-Der Schiffer D536 (Mayrhofer)

-Standchen (Hark, Hark the Lark)

*Schumann Soprano Lieder:

-DER NUSSBAUM

-Frauenliebe und Leben- Helft mir, ihr Schwestern

-MIGNON (KENNST DU DAS LAND)

-AUS DEN -STLICHEN ROSEN

*Rachmaninov - Dream

2.Opera songs :-

*Gluck - Orfeo ed Euridice - che faro senza

*Mozart - Don Giovani - Il mio tesoro intanto

*Mozart - Don Giovani - Fin ch'han dal vino

*Rossini - The Barber of Seville - Largo al Factotum

*Rossini - The Barber of Seville - Una Voce Poco Fa

*Rossini - La cenerentola - Un Segreto D'importanza.

*Puccini - Tosca - E Lucevan Le Stelle

*Verdi - Don Carlo - Sotto ai folti immensi abeti

*Verdi - La Forza Del Destino - Pace, pace, mio Dio! (Amazing!!)

*Verdi - Il Trovatore - Squilli, echeggi la tromba guerriera

*Verdi - La Traviata - Sempre Libera.

Sure there are other huge works , this what's coming into my mind right now!!

My favorite classical "song" is the "Ode to Joy" from Beethoven's Ninth Symphony. What a joy and what a rush it is to hear that piece played by a world class Symphony Orchestra!

If an operatic aria counts as a "song" then perhaps "Un del di vedremo" from Puccini's Madama Butterfly.

[I'm betting however that you don't mean a song, you probably mean any classical piece. Songs are for singers! The Moonlight Sonata is not a song!]

Lay Lady Lay

Bob Dylan

Assemble All Ye Maidens, which was a song set to music by Gustav Holst.

Mozart's concert aria Ch'io mi scordi di te (K.505), written as insertion aria to the opera Idomeneo. It's a superb musical dialogue between the soprano voice and the piano. http://www.youtube.com/watch?v=1zZ3vdXIl1o

Candle In The Wind

Elton John

Beethoven's Moonlight Sonata

My Generation

The Who

Beethoven's Ninth Symphony Op. 125, especially the first movement "Allegro ma non troppo, un poco maestoso".