Nice idea for a thread!
I will list bands, not just albums.
Very early on:
Sgt Pepper’s - informed me that rock could be a bit more than 3 minute, 3 chord, songs.
Next:
Deep Purple - In Rock, Black Sabbath- 1st, Uriah Heep - Very Humble, and others - informed me that rock could be even heavier, and be bit more focused on musicianship
Next:
T2 - It’ll All Work Out in Boomland, YES - The YES Album, King Crimson - ItCotCK, ELP, Gentle Giant, - informed me that rock could totally break free of it’s blues roots, and that there is an entirely new level of musicianship and complexity from the previous bands I listened to.
Very soon after:
Bands - PFM, Banco, Le Ormer, Triana, Grobschnitt, Museo Rosenbach, many more - informed me that world class prog, as good as what was coming out of England, was being made all over the world, and that those countries put their own cultural spin on it.
Around the same time:
Discovery of fusion, like - Mahavhishnu Orchestra, Return to Forever, Brand X, Iceberg - While not exactly the same as prog, the creativity and musicianship was there.
Next:
Henry Cow - Unrest, Univers Zero - Heresie, Art Zoyd - Generation sans Futur - informed me that atonality and dissonance had it’s place in music. Soon to be followed up with most of the rest of avant-prog.
Stravinsky - Rite of Spring, Bartok - Music for Strings, Percussion Celeste - Informed me that classical could be more than all the famous warhorses that I found boring. This lead directly to the even more avant-garde composers - Scheoenberg, Elliott Carter, Berg, Joan Tower, Charles Wuorinen, etc.
