From that era, I would go for any Yes album until 1980s. Then it gets way less progressive.

I recommend albums I know and love:

• Emerson Lake & Palmer: “Tarkus” and “Brain Salad Surgery”,
• Genesis: “Selling England by the Pound”,
• King Crimson: “In the Court of the Crimson King”, “Red”, “Discipline”,
• Van Der Graaf Generator: “The Aerosol Grey Machine”.