Well, here are my 20th Century picks based upon a categorization technique
adopted from art historian Jean Clay.

The Liberation of Orchestral color, (from harmony, melody, rhythm, and
form): Ligeti's "Atmospheres."

Distortion of the Classical Canon, (march, waltz, chorale, fanfare, etc.):
Mahler's 7th Symphony.

The Pulverized object, (the music is decomposed into "moments" and linear
motion is abolished): Stravinsky's "Right of Spring."

Frontality I, (step-by-step organization dictates form): Stockhausen's
"Kontakte."

Frontality II, (the *lack* of organization dictates form): Cage's 4'33"

The Real Object I, (taped sounds, manipulated or not), are incribed into
the coherence of the work): Boulez' "Repons."

The Real Object II, (the work explodes under the presence of the imported
taped sounds): Varese' "Deserts."

John Smyth