There's this piece of classical music that I've heard a few times whose title or composer elude me. I assume it's a classical work, for a fairly shaky reason (see below), and not a "showtune" or Original Motion Picture Soundtrack.

I believe it to be a work intended for the piano as I heard it being played on one of those kiosks at a Fry's store (in the classical music section). I've also heard it performed by a chamber orchestra as incidental music in an episode of The Simpsons; it was repeated several times throughout the episode, and it was played during some sad bits.

It's a slow, sad tune.

I have this Classical Masterpieces of the Millenium boxed set (given as a gift) with twenty fucking CDs full of music by twenty classical composers. Not one of them has the tune I'm trying to dig up.