Great thread! Lots of stuff to research.
Seems the tag “progressive” means something different to most of us.
One that hasn’t been mentioned yet that I really enjoy is Klaatu self-titled. Side A if I had to pick one.
Best progressive rock album side
My intent is to seek albums which I may not own from the recommendations of you all. I ranked best sides of progressive rock albums on vinyl that I own and came up with the following list. I don't want it to undermine anything else that an artist has created. I love it all but as far as start to finish on one side this is what I came up with.
#1: Supper's Ready
#2: Terrapin Station
#3: Atom Heart Mother
#4 The Court of the King Crimson
#5 Echoes
Of course there are many more. Some may not be complete sides like Atom Heart Mother but the intent of the artisan was to make it a complete side. I had a very hard time deciding between #1 and #2. Both are very worthy in my mind.