What a great thread. Paying attention to music and recordings is far more productive than obsessing over equipment!
My first entries, in no particular order:
1) Master of Reality- self titled. This is a fairly little-known band whose second album actually had Ginger Baker on drums. But this is one of the best Redbook CD's that I own, and "Kill the King" is one of my references for depth and detail. Excellent Texas blues/rock.
2) King Crimson- Lizard. The Steven Wilson re-master is brilliant, taking a so-so album and turning it in to a masterpiece. All of the Crimso remasters are outstanding, but this one is mind-blowing in how it turned out. I would list all of the remasters, but I'm trying to restrain myself.
3) Cowboy Junkies- Trinity Session Yes, Trinity Revisited may be technically superior, but the original is stunning in the lack of pretense.
4) Porcupine Tree- In Absentia Again, I could list them all, but "Trains" is a reference recording for me, both main stereo and headphones.
5) Kyuss- Welcome to Sky Valley I'm going on a limb with this one, and it is certainly not an audiophile recording. But it is as close to a live recording as one can get, and still be in the studio. There is a ton of depth amidst the distortion, and this is the defining album of the whole Stoner/Doom/Dessert Rock genre. But one has to REALLY be into down-tuned distortion to 'get it'
Thanks for all the suggestions so far. I hope there are thousands more to come...