OK, time for me to get off the stick and add to this thread.
Starting with classical, somebody mentioned Reference Recordings. Here a few of may favorites from Professor Johnson:
Eiji Oue & the Minnesota Orchestra: Mephisto & Co.
Michael Stern & the Kansas City Symphony: Saint Saens Symphony No. 3 "Organ"
Tafelmusik: Popular Masterworks of the Baroque
All three are available on both 45 RPM vinyl and CD and/or SACD (although the Tafelmisk vinyl was issued in the 80s and is a bit tough(and pricey) to track down right now.
Mussorgsky: Pictures at an Exhibition & Rimsky-Korsakov: Scheherazade - my two favorite recordings of of both of these pieces are the Reiner/Chicago Symphony and Ansermet conducting D'Orchestre de la Suisse Romnade. Different reading but both outstanding in their own way.
The Reiners can be found at Acoustic Sounds on 33 or 45 vinyl and SACD Hybrid Discs and are curerently in print. The Anasermets are a bit tougher to get your hands on. issued on audiophile vinyl as part of the King Recors Super Analogue series in the mid 90s, but they were only sold in Japan and are tough to find. Decca record did a nice job reissuing them as part of their Eloquence line of CDs and although the series is imported from Austrailia they are fairly easy to find on eBay at pretty reasonable prices.
And speaking of Ansermet, one of his best recordings was a 2 LP set done with The Rpyal Opera House Covent Gardens Orchestra called The Royal Ballet - Gala Performances. This album was originally released as part of the RCA Soria series, but Acoutics Sounds Analogue Productions label currently sells 33 RPM amd SACD versions of it (and I am told a 45 RPM set in in the works for later next year. ) This album is also available in the Eloquence , not as good sound as the AP version, but you can get if for a fraction of the price.
Two more that I recommend from the Analog productions series or RCA Living STereo reissues are Alexander Gibson /Royal Opera House Covent Gardens Orchestra Gounod's Faust& Bizet's Carmen and Fiedler and the Boston Pops doing Gershwin's Rhapsody in Blue. Both have outstanding sound in addition to great music.
The Dvorak Cello Concerto featuring Janos Starker with Antal Dorati conducting the London symphony has long been one of my top of the pile recordings and is fairly easy to find in digital or vinyl (Analog production just previewed a test pressing of an upcoming 45 RPM release of this album at the recent NY Audio show. I was not there that day, but have been told that it was outstanding. I'll be one of the first on line when that comes out.)
My last classical selection for now is Rachmaninoff's Symphonic Dances by Donald Johanos and the Dallas Symphony Orchestra. Originally issued on Turnabout record it was redone as an audiophile in the 90s by Athena Records and then again more recently by Analogue Productions. Not all that easy to find, but if you ever see one do not pass it by.
Jazz is a bit tougher to recommend because there as so many different variants of its and many people have strong feeling about one ov the other. I personall a m most into mid 50s to early 60s jazz and the artists who were big back then.
Three records I would recommend to get you started are Gentle Ben by Ben Webster, Ella Fitzgerald's Let no Man Write my Epitaph and of course Mile Davis Kind of Blue. Luckily, most good jazz albums have been reissued many times over the years so it is fairly easy to track down copies. I may take some work to figure out and then find the best sounding versions, but if you want to start by just getting an appreciation for the music, they are fairly easy to find.
The other thing that I would recommend it to be on the lookout for albums by Pablo records. Pablo was started in the by Norman Granz of Verve in 1973 sand featured many of the great artists from they heyday of Verve. People like Oscar Peterson, Ella Fitzgerald, Joe Pass and Dizz Gillespie. I have heard many people say that it was a bunch of old guys past their prime, but I think of it more as a collection of Grand Master who ahve worked for years to fine tune their craft to perfection. Pablo features tons of great music but they are not considered desirable by the collectors market so you can pick them up for a small fraction o=f what you would have to pay for original Verves and Blue Notes.
This is just the tip of the iceberg, but I hope you have fun getting started. Keep in mind that as you go you will encounter all kinds of different stuff in both classical and jazz music that you may really like or really detest. On of the quickest and easiest way to get familiar with all of the different artists and styles is to sign up for a Tidal (or if they ever get it together and launch in the US) a Qobuz account and then just try things out without having to pay for each album. The $20 - 25 a month you have to pay for the subscription is probably less than you would pay for two CDS and you can listen to 100s of different ones each month. It is a great way to explore.
And most of all, HAVE FUN!!!!