There is something special about that era to me- UK from say the mid-'60s to the early '70s- where the psych/rock/folk stuff merged. John Martyn, Fairport Convention. I listen on vinyl, so some of these records are now very expensive or not so easy to find in great condition as original early pressings. But the artists weren't as constrained in some ways by genre. Much got labelled after the fact as "prog" simply b/c it didn't fit neatly into one slot. I gather it was a relatively small community at the time too- a lot of these guys were not only influenced by each others' recordings, but knew each other. To me, this is one of the most exciting periods in modern "pop" music and though some of the keyboard based prog now sounds dated, e.g. first ELP album, it's still cool to listen to. Fairport's 'What We Did' is another record it took me time to appreciate- I knew Liege & Lief, which is always heralded as their 'best' b/c it is more UK-centric but "What We Did" which is regarded as more "American" is brilliant. The price of a minty orange bulls-eye pink label UK is now obscene, though. Have no idea how well it was rendered digitally, but it is also worth checking out. (And as you may know, Sandy Denny was one of the few to actually sing on a Zep recording).
