The Premier League:
Atomic Rooster
Emerson, Lake and Palmer
King Crimson (prior to Discipline)
Manfred Mann's Earth Band
Pink Floyd
UK
Yes
Wigwam
The Rest of the League:
Anyone's Daughter
Aphrodite's Child
Argent
Barclay James Harvest
Birth Control
Camel
Curved Air
Dream Theater
Electric Light Orchestra
Eloy
Focus
Fruup
Genesis (with Gabriel)
Gentle Giant
Gong
Greenslade
Guru Guru
Steve Hackett
Hawkwind
Steve Hillage
Illusion (Renaissance)
IQ
Jane
Kansas
Moody Blues
National Health
Nektar
Novalis
The Nice
Mike Oldfield
Ozric Tentacles
Pallas
Alan Parsons Project
PFM
Quintessence
Refugee
Renaissance
Todd Rundgren's Utopia
Spock's Beard
Spooky Tooth
String Driven Thing
Supertramp
Transatlantic
21st Century Schizoid Band
Uriah Heep (with Ken Hensley)
Vangelis
Rick Wakeman
Yellow Matter Custard
Depends whether you consider them progressive:
Ambrosia
The Byrds
The Beach Boys
The Beatles
City Boy
Fifth Dimension
Golden Earring
Home
John Miles
Jethro Tull
Man
Roxy Music
Rush (first six studio albums)
Wishbone Ash
Frank Zappa and the Mothers of Invention
Has anyone started a comparable favourite heavy rock band list?