Even limiting the discussion to CD, the list is, functionally, endless. Picking things that have not shown up in posts (yet), and in no particular order:
Roberta Flack - Quiet Fire. Plain-ol' catalog release. Sounds straight off the three-track master. Demo: Get Up Moses.
Rhythm Devils - The Apocalypse Now Sessions. On Ryko, and maybe out of print. All percussion, big room sound, and electronics that separate Those That Can from Those That Can't. Demo: Napalm For Breakfast.
Bad Company - Bad Co. An Audio Fidelity gold disc, mastered by Steve Hoffman. Demo: Seagull. Hell, the whole disc.
Leon Russell - Leon Russell. A DCC gold disc, mastered by Steve Hoffman. Demo: A Song For You.
Cowboy Junkies - Trinity Sessions. Another Plain-ol' catalog release. Besides demonstrating why Ambisonics is everything Dolby Anything will never be, this disc is an excellent soundstage/depth/placement test. Demo: All of it.
And here's where it gets to something like shooting fish in a barrel. I've picked up two titles on SHM-CD, Stanley Turrentine's 'Stan "The Man" Turrentine,' and the Rolling Stone's 'Let It Bleed.' Having A/Bd the Stones record against the DSD remasters, the new plastic/process makes an embarrassingly huge difference. No, it doesn't make a CD sound like an SACD, but the SHM-CD way of doing things definitely leaves a regular CD in the dust.
In short, I think all of our favorite demo lists are in for a major re-write.