Classical would be a long list. In lieu of that, I'm just going to give links for the biggest reissue series.
Sony Classical
A lot of these are hard to tell; I can't confirm if they actually used the quad mix, and in several cases probably didn't. The Schippers/NY Phil Alexander Nevsky/Pictures at an Exhibition and Bernstein conducts Copland are modern mixes from 3-track tape, I believe.
- Boulez Conducts Bartok (did not use quad mix)
- Boulez Conducts Ravel
- Bernstein Conducts Holst (The Planets) and Britten (did not use quad mix)
- Bach: The Four Great Toccatas and Fugues (E. Power Biggs)
- Tchaikovsky: Symphony No. 4 (Bernstein - Nutcracker Suite on Disc is pre-quad)
Deutsche Grammophon
These are the ones done by DG itself, not Pentatone. In all cases these discs have a surround mix that is believed to be sourced from Quad, since a quad mix was never released it's impossible to know for sure - not positive if the center channel is muted or artificially created. To be clear, not vouching that these are all from quad, but it would be surprising if they weren't.
- Karajan - Mozart Requiem
- Karajan - Beethoven 9th (70s recording, not the complete set from 63 also on SACD)
- Kleiber - Beethoven 5th and 7th (also on blu-ray box with his other orchestral recordings for DG, unclear is the Schubert 3rd & 8th in that set is an upmix or from a quad)
- Kleiber - Verdi: La Traviata
- Pollini - Chopin Polonaises
EMI/DTS Entertainment
DTS CDs with a muted center channel, released in 1998.
- Karajan: Tchaikovsky Symphonies 4-6 (one per release), Mozart: Symphonies 35-41 (two per release, excluding 37 which is actually by Michael Haydn)
- Boult: Tchaikovsky Orchestral Suite No. 3
- Villa-Lobos conducts selections from his Bachianas Brasilieras
- Paavo Berglund/Bounmouth SO: Grieg's Peer Gynt Suites and other Nordic works.
- Martinon: Complete Orchestral Works of Debussy (five releases)
- Previn/LSO: The Planets
- Muti: Aida (Caballe, Domingo, etc)
EMI
24/48 DVD-A 2 sided discs (other side is a DVD-A with DD and DTS tracks)
- Previn/LSO: The Planets
- Mackerras: Handel Fireworks and Water Music
- Previn: Messaien's Turangalîla-Symphonie
- Kempe: Strauss's Also Sprach Zarathustra and Alpine Symphony
- Cleobury: Bach Magnificat
- Martinon: Ravel Orchestral Works (Bolero, La Valse, Daphnis)
- Karajan: Wagner Overtures & Preludes
- Previn: Waltons Belshazzar's Feast, 1st Symphony, & Scapino Overture
Supraphon
A surprising number, all Japanese releases - listed here:
http://www.hraudio.net/music.php?format=10&genre=0&label=582&page=1
Vanguard
Most Vanguard SACDs had two releases, once through Artemis and once through Omega. The Omega releases came first; the only thing to be aware of is that the Omega release of the Berlioz Requiem has a defective mix, fixed in the Artemis release.
They're listed here:
http://www.hraudio.net/music.php?format=10&genre=0&label=35&page=1
Classic Records also released the Berlioz Requiem in quad DVD-A; their only quad release.
Silverline/Vanguard
Silverline re-released many recordings made by Vanguard in 5.1 surround sound as DVD-Audio discs. They advertised these discs as being from quadraphonic sources, but in reality only some of them were, and there's never been complete clarity on this point. Most of these were also re-released as dualdiscs, again by Silverline. I have not included a few older recordings that are clearly not in quad, notably the Adrian Boult and Pierre Monteux discs, as well as the recording of Prokofiev's Lt. Kije Suite and Peter and the Wolf with Boris Karloff narrating. I also originally included the three symphonic recordings done by Sergiu Comissiona in the list but subsequently removed them, when a little sleuthing revealed that these were actually very early digital recordings. Silverline does not have a great reputation for honesty about their sourcing, but at least these discs all include a high-res stereo track as well. It's a darn shame, because there were plenty of Vanguard quad recordings that need a re-release:
http://www.surrounddiscography.com/quaddisc/quadclas.htm#V
(All with Maurice Abravanel, Utah Symphony)
Brahms Symphonies 1-4 (complete), Haydn Variations, Overtures (3 releases)
Sibelius: Symphonies 1-7 (complete) (3 releases)
Mahler: Symphonies 1-6 (6 releases, 5 & 6 on dualdisc only). 1, 3, 5, & 6 were released on quad, 2 & 4 were pre-quad recordings.
Tchaikovsky: Swan Lake & The Nutcracker (one release each)
RV Williams: Symphony No. 6 etc
Rachmaninoff: Symphony No. 3
Disturbingly, except for four of the Mahler Symphonies, it does not seem that any of the rest were originally released in quad, according to the quad discography. It is plausible that an unreleased quad mix existed for some of them.
Pentatone
The big one; they've heavily mined the Philips quad vaults, and also dipped into Deutsche Grammophon.
Dutton/Epoch
The new player in town, from the Sony vaults:
http://www.duttonvocalion.co.uk/products.php?cat=3
Mobile Fidelity
8 Releases:
http://www.hraudio.net/music.php?format=10&genre=1&label=60&page=1
This is mostly off the top of my head, what did I miss?
Edited to add MoFi and fix typos.
Edited again to add more DTS CDs
Edited again to add Silverline