Important classical music

On Facebook this morning a dear college friend asked what we thought were some important pieces of classical music: "A question for all you musicians out there.. In your opinion, what are a couple of the most important or profound classical works? This is either from your perspective, from the composers perspective in relation to their body of work, or from a historic perspective as an influence on the development of classical music."

I was genuinely STUNNED! At first, it was real hard to narrow down, second, not repeating the multitude of answers already posted was tough (actually, couldn't do it), and third, the incredible range and reasons for my answers impressed even I! Not only that, but I ended by stupidly saying "Let me know if you want more"! ???????? Am I really that geeky? (Don't answer). I could go on and on and on and on and on and on with this list, but she only wanted "a couple". Failed at that, too. I love it, though. This was a FUN exercise. Thank you, Sally!

SPB's list:
Milhaud - La Creation De Monde (classical+latin=jazz before Gershwin did it);
Copland - Appalachian Boing;
Shostakovitch - Festive Ov (You can be depressed, repressed and Big Brothered but still write joyful music);
Coates - Calling All Workers (Woah!);
Beethoven - 7:2 (You can be deaf, mad and smell but still write expressive music);
Glass - anything;
Part - Cantus In Mem... Ben... Britten, or Ravel - Bolero (both incredible 'exercises');
Sure about Ives? He was an insurance agent, and an organist to boot.
Risky Korsettes Off - Scheherezade (orchestration);
Kodaly - Hary Janos Suite (love the opening sneeze);
SOUSA! (Ok, there's a reason his songs and operas didn't survive, but you don't HAVE to mention them);
Prokofiev - Peter & the Wolf;
Mozart - Feeeeegaro (ov &/or opera);
Janacek - Katya Kabanova (a bit sad, though).

How would YOU answer that question?