Best Sounding LPs

Dire Straits "Brothers in Arms" works for me.

The best sounding jazz-pop lp, which I use as a reference, is Donald Fagen's "The Nightfly." I have the Quiex-2 version. Terrific.

Jazz - Coltrane's Blue Train on 45rpm.

You mentioned folk and country . Jazz and classical seemed to be pretty well covered here so I will list some great folk, bluegrass, rock recordings. All of which can be found new.
In folk:
Greg Browns "Poet Game"
Doc Watsons "Southbound"
Alison Krause and Union Station
Joan Baez's "Angeline", "Diamonds and Rust"
The Weavers "Live at Carnegie Hall, 1963"
Harry Belefonte "Live at Carnegie Hall"
In Blues:
Muddy Waters "Folk Singer"
The Anne Arbor Folk and Blues Festival
Doug McLeod "Hard to Find" (this one you will have to get used)
Rock:
Pink Floyd "Dark Side of the Moon"
Any of the Led Zepplin reissues
All the Bob Dylan reissues
All the Peter Gabrial reissues
Beach Boys "Pet Sounds"

George Waters "Amused to Death" (nothing to compare with, #1)
Purim,Moreira "Dafos"
Pink Floyd "Final Cut" Japan
Dire Straits "Love over Gold" and "Brothers in Arms"
and a look to:
http://www.tnt-audio.com/topics/fav_e.html

Many thanks to all who replied. My shopping list is long!