I'm thinking of stuff like Who's Next, Led Zeppelin IV, Deep Purple in Rock, etc. Do you have other examples of classic rock albums that are close to the edge of prog?

The Incredible Sting Band—ITKOS

Black Contry Communion—IV

In the northeast of the United States and around Boston, Quill was a well-liked local attraction. Almost every member of the band could play many instruments, and they had a habit of switching them up while performing. At any moment during a set, guitarists and keyboardists will switch to horns, cellos, or woodwind instruments. Aside from being unexpected, the music itself has a unique, purposefully bizarre sound that falls between early British progressive rock and American psychedelic rock. The songs themselves have equally ridiculous titles, and the band members are all credited under wigged-out pseudonyms. The most noticeable instrument is frequently the bass guitar. Sonically, it's sparsely realised despite the performers' diverse skill sets, filled by barely audible organs and pianos as well as mixed-back guitars and drums. 

 The arrangements seem to be casual and improvised, a style that can only be achieved with extremely meticulous planning and orchestration. Loaded with social satire, the lyrics depart significantly from the popular hippy abandon of the time, and the backing tracks feature an odd assortment of chord progressions and modulations. The way it transitions between songs, and sometimes even within a single track, can be erratic.

They performed at Woodstock in 1969, but owing to technical difficulties, only a few minutes of their performance were filmed. Thus, Quill didn't feature in the Woodstock movie. Probably the destiny of this gifted band would have been very different if they had been in the film. Following the release of their self-titled album in 1970, they broke up. 

To avoid mentioning repeats... I want to say classic Moodies or Procol Harum

I think both are progressive rock, call them art-rock, crossover, proto-prog, all these tags are correct IMO. 

I can't argue with that, but...

Some users already mentioned the likes of Who, Uriah Heep, etc... so I didn't figure I was off the ball

Where do we draw the line? The eternal question bears repeating I guess 

A few Uriah Heep albums fit under heavy-prog, others are just hard rock. 

My bad, hope this thread does not reach the "what is prog?" arguing again... 

The Who

Queen

Supertramp

Radiohead

Deep Purple

Rainbow

Sabbath

Tull

take your pick

Abbey Road by The Beatles

The 5th Symphony by Beethoven.

Toccata and Fugue in d minor by JS Bach

"Force It" by UFO 

"Captain Beyond" by Captain Beyond

"Queen 2" by Queen

...and so forth.  Lots to choose from. 

Tubeway Army - Replicas

Al Stewart - Year Of The Cat

Iron Maiden - Somewhere In Time

Public Image Limited - Album

Propaganda - A Secret Wish

Wishbone Ash - Argus

Mansun - Six

Radiohead - OK Computer

Simple Minds - Street Fighting Years

Led Zeppelin have several proggy tracks but imo don't really have one full on "proggy" album. PG probably comes the closest though or maybe Houses of the Holy.

YES!!  Great suggestion!!  I've long thought the same thing!  

https://alicecooper.com/music/killer/" rel="nofollow - https://alicecooper.com/music/killer/

The Steve Miller Band's 1968 album "Children of the Future" was recorded at Olympic Studios in London under the direction of legendary English producer Glyn Johns. With a hint of Summer of Love psychedelia mixed with West Coast sound, Side One was mysteriously veiled in the hazy artistry of the British progressive rock ethic. 

The first track is the title tune. It's bluesy, exploratory, and has elements of folk-rock, yet it also fits in nicely with the progressive music era. The title track's keys and swirls give way to "Pushed Me Through It" and the mellotron-driven prog-rock song "In My First Mind," which flow into the epic, hazy, lazy, organ-infused "The Beauty of Time Is That It's Snowing," which fluctuates in unexpected ways. Side One of the "Children of the Future" LP, which is listened to as one suite, is one of the best works that the Steve Miller Band has ever done and is one of the best examples of early progressive rock.

The music on Side Two is more in line with "normal" blues-rock music. However, it is just as delicious as side one. To kick things off, we have my all-time favourite Boz Scaggs song, "Baby's Callin' Me Home," with its majestic acoustic guitar and harpsichords. "Steppin' Stone" features strong rock music from the 1960s, while "Roll With It" is another rock song about life on the road, including sharp guitars, a swaying organ, and Steve singing from a very high place. "Junior Saw It Happen" is the most vibrant of the final three songs. Ben Sidran's harpsichord performance on "Baby’s Callin’ Me Home" is peculiar, but Miller's mouth harp on "Key to the Highway" is fairly awesome.

 

One of the first bands ever to present their music as a seamless flow of sounds rather than a collection of individual pieces was The Electric Flag on their first studio record. This sounds proggy, doesn't it?

Well, released in April 1967, "The Trip: Original Motion Picture Soundtrack" is, due to its structure and the year it was released, certainly a progressive music effort, yet in an American way. Consisting of 18 tracks, the album features an eclectic variety of musical styles, from epic scores ("Peter's Trip") to acoustic wanderings ("Joint Passing"), odd circus-like music ("The Other Ed Norton"), pliable floating substance exhibiting hallucinogenic effects ("M-23"), wild saxophone solos set to furious jazz rhythms ("Peter Gets Off"), electric-violin mood swings ("Synesthesia"), fluid fringe (as in "Flash, Bam, Pow "), trippy states that limp ("A Little Head"), reeling welters ("Fewghh"), a fierce improvisation of blues-rock ("Gettin' Hard), but once the mists lift, we're treated to breezy horn -based tunes ("Green and Gold"), and a wild seven-minute jam called "Fine Jung Thing" as well.

Moreover, "The Trip" is among the first rock records to use the Moog synthesiser, brought by electronic music pioneer Paul Beaver.

Boston- Boston

Supertramp- Even in the Quietest Moments

The Beach Boys' "Pet Sounds" (1966) is regarded as a progressive album in large part due to its avant-garde production methods. The album's inspiration and driving force, Brian Wilson, pioneered experimental techniques in music production. Pop, jazz, classical, and avant-garde elements were all combined into the record to create a distinctive and sophisticated sound that went beyond the bounds of conventional popular music. 

At the time, standard pop and rock music lacked the intricate orchestration and instrumentation found in "Pet Sounds." Wilson gave the songs additional levels of texture and depth by using unusual instruments like soda cans, flutes, French horns, bicycle bells, and electro-theremin. The elaborate vocal arrangements and harmonies demonstrated a degree of musical intricacy that has never before been heard in mainstream music. 

The narrative arc and intellectual coherence of "Pet Sounds" are two other elements that distinguish the album as progressive. In contrast to traditional albums, which were merely collections of single songs, "Pet Sounds" was intended to be a single, seamless piece of art in which each song added to the overall theme. The songs on the album flowed together harmoniously, telling a narrative and evoking distinct feelings all at once. This was achieved through the connections between the songs' melodies and lyrics. 

Overall, "Pet Sounds" is a breathtakingly beautiful album. The tunes resemble hymns in their purity and spirituality. For the period, the instrumentation was crazy, the density was novel, and the harmonies were astounding. It may seem uninteresting in comparison to other musical eras, but that's only because it was so influential and widely imitated that it defined popular music for the following decades. 

I don't see how Supertramp aren't prog. They are even on this site as crossover prog. That album even has the very much prog "fool's overture." There's even a case for Styx who are also on here but as prog related. Boston maybe not so much but even that first album has it's moments. Maybe semi prog should be a thing but again you'd have to have a pretty snobby attitidue about what is and what isn't prog to not consider Supertramp to be some kind of prog imo.

Smoking is rather Deep Purplish with it's long instrumental part with organ so to me that's rather proggy also.

The Coop's proggy nature can be seen much earlier. I already mentioned the album Killer, but you can hear the band's prog-leanings on several songs from both Love It to Death and School's Out. I'd mention Easy Action, but I think their longer songs on that album were more acid rock/psychedelia.

https://www.youtube.com/watch?v=VxotPAO7mZ0

 

Oh yes, Alice Cooper's proggy nature can be heard on School's Out and Billion Dollar Babies, two other albums that I have. I wonder if anyone has ever considered Alice Cooper for inclusion on this site.

 

That might be wishful thinking on your part. Progarchives labels them prog because it's a label that fits not because they are trying to shoehorn them in some place they really don't belong (which could be the case with some artists on here such as Tori Amos). But it's not just PA that considers Supertramp to be prog. Allmusic, rate your music and Wikipedia all have them tagged as prog. Maybe where the confusion comes in is that their music falls under other genres (subgenres) as well unlike say King Crimson who are pretty much just progressive rock and not much else.

Not laughing, 70s Judas Priest was proggish in places, also the great Simon Phillips played drums on one of their albums (Sin After Sin, 1977). 

 "Travelling underground" by Ian Lloyd & Stories, the first Cockney Rebel album; Angel by Angel, "Helluva Band" by Angel; "Level Headed" by Sweet; Alice Cooper: "School's days", "I'm eighteen"; Amboy Dukes: "Marriage on the rocks/Rock bottom"; Bull Angus: "Bull Angus", "Free for all"; Charisma: "Charisma", "Beasts and fiends";  Citadel (USA) "The Citadel of Cynosure & Other tales", many, many more I'll leave it for another time.

I fully agree with this album's inclusion! Don't think for a moment of their early hits: this one has string sections, harpsichords, horns, swirling synthesizers, and a Mick Tucker percussion solo on the almost-instrumental extended album closer, "Air on 'A' Tape Loop". Still, there's just enough loveable nuttiness included to remind you that it really is the same band that did "Ballroom Blitz". If you were too young to remember the 1970s, just listen to Level Headed - this album says what words can't!