I went to town on this one -- most of the instruments are part of the extended instrument set. This will still sound OK on a General MIDI device, but on the XG (and presumably on any GS-compatible wavetable), it really comes alive. I'm using three different pipe organ sounds, for the two manuals and the pedals; two different versions of slow-strings (neither of which is the default bank), for the melody and countermelody; and a slow-attack violin for the solo.
I've long believed this to be the most beautiful piece of music ever composed.
It's by Tomaso Giovanni Albinoni. You've no doubt heard it used in various places before.
Like the Kiki's Delivery Service file, I did not make this MIDI file, but modified its instrument registration (well, for Kiki I also corrected the tempo) to support instrument sounds beyond the antiquated General MIDI standard.