Best progressive rock album side

@mapman - should be a new P.T. album coming out very soon; have you read Steven Wilson's autobiography yet? Excellent read! 

Bowie Ziggy Stardust - pick a side

I'll go with The Pineapple Thief's "Versions of Truth". Deep into their catalog right now as I am going to their show in a few days.

OP by @ricmci "My intent is to seek albums which I may not own from the recommendations of you all."

So many great prog albums already listed, here are some that I really enjoy and may be obscure to some.  @ricmci, hopefully I've introduced you (and others) to some new prog that you will enjoy.  Links included.
 
Progressive Metal
Riverside - Anno Domini High Definition (also called ADHD)
https://open.spotify.com/album/2BJkbdmzqURLLnS6xQBmlA?si=9o401RaPTCicjZggHi8NOw

Experimental Post Metal
Indukti - S.U.S.A.R.
https://www.youtube.com/watch?v=dufJczX_PH8

Crossover Prog
Steven Wilson - Grace for Drowning
https://open.spotify.com/album/44uwH9ASkm1MStvYdDdTDn?si=1Fo9edF_SvG0mlmjS1Y9mw

Steven Wilson - The Raven That Refused to Sing (and Other Stories)
https://open.spotify.com/album/2xJFvV7JzoYYMere5rqjVf?si=rS79XoEnRIqE7KryKqqTbg

The Pineapple Thief - 8 Years Later
https://open.spotify.com/album/1bPaM4vbjgWkyKgsooeSiH?si=LtnKF1dVTRG7e4U--LbqGQ

Atmospheric doom metal/post-rock
Kauan - Sorni Nai
https://open.spotify.com/album/5PvChfV6UTytiRuwsoOx4V?si=nOamb__STwWgMWVzsjWy-Q

Finnish Folk Prog (I believe?)
Kohti (collaboration betweem Antov Belov and Marja Mattlar)
https://open.spotify.com/album/3217CFw6R6xOdvjcwTsXAf?si=IWpfIT2tQySVmcF_4gj7gw

Ambient/Prog/Classical 
Antov Belov - Piano Works 1
https://open.spotify.com/album/6oVDzb2GGAlm18hil5hWqn?si=fskThYSsQ5mkOv4eZyGz1w

I’m no guru of prog, I lived through the original classical formalism and have the UK early pressings of ELP, Crimson, Yes, etc. But I tapped into "prog guru" Ken Golden who helped broaden my horizons, with good King Records reissues from Japan of some of the "important" Italian prog, and other things I found along the way (an Italian Polydor of DeDeLind, which sounds like Fado music meets Deep Purple).

Among them, an interesting obscurity out of Denmark, circa 1971, called Blast Furnace (band name and album title). An OG pressing will be spendy but it was reissued w/in the last five years- worth seeking out.

I also very much like both Cressida albums on Vertigo Swirl, from the period. Those will be spendy. I opted for a German pressing of Asylum, have the UK of the first album.

There are certainly different categories of prog, including pretty deep offshoots.

I really liked Ollie Halsall’s vibraphone-like touch to the guitar on the first two Patto albums (the US copy of the first record is more bombastic than the UK Swirl and far cheaper)- on their second, I’d say you need to look outside of the US for copies from elsewhere.