Art Rock is "Progressive" Rock's cool brother and for good reason. In place of Progressive rock's seeming contempt for rock music and aping of Renaissance and Jazz musical ideas (almost always in the most cliched ways possible showing as much lack of understanding of those forms as they do of Rock& Roll), Art rock builds on the various ways Rock music separated itself from the Blues/R&B beginnings of Rock & Roll in creative and original ways. King Crimson's first album is a landmark in this regard and is probably responsible for the horrible Progressive and Progressive\Metal bands that followed. Still, "The Court of the Crimson King" and "21st Century Schizoid Man" are as amazing a re-imagings of Rock music as Jimi Hendrix's work. Like the first King Crimson album and especially on their albums "Led Zeppelin IV" and "Houses of the Holy" Led Zeppelin managed to incorporate pre-20th century british folk and some Jazz influence
("The Rain Song") to incredible effect as well as consistantly delivering hard rock songs of the highest quality.
The following music truly is progressive.