Best Sounding LPs

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!

Man-oh-man, don't know how I missed this thread. My mouth is watering...
About all I can add to the fabulous responses above:

Any jazz on Japanese label Three Blind Mice
Another Canadian Holly Cole LP - Romantically Hopeless, this one includes a bonus 12" 45rpm w/amazing cover of Paul Simon's "One Trick Pony"
Louis Armstrong - Satchmo Plays King Oliver reissue (45rpm or 200g CLassic Records)
Best cheap domestic folk/rock beachy,happy hour music: Jack Johnson - Brushfire Fairytales
Cheers, Spencer