I have very little classical music in my music library, mainly because I always struggle to know what to buy/download.

What are "Musts" for the collection?

There are several ways to do this:

1. Classical radio stations like to poll their listeners and come up with a "top 100," which means 100 most popular. Typically these lists have many pieces like "Pachelbel Canon" that classical music snobs (like me) don't consider to be "must haves."

2. Snobs compile lists of what we claim are the "highest quality," even if these lists don't have all of the best-sellers.

3. Pinhedz go even farther, and list things like Henry Purcell's Fantasias for viols, which make the list only because the pinhed personally likes them.

Another feature of this kind of list is that they are typically 100 or more if the compiler really includes everything considered to be in the "must-have" category, because there are about 100 composers in the top-notch category, each of whom produced several masterpieces. That would require several shopping trips, so I'll list something more scaled-down.

This is a mixture of radio station "top 100" selections, along with some snob/pinhed selections (which I'll put in bold type, because they're really the best):

I don't know if you like baroque, but here's some:
[Purcell -- Fantasias for viols]
Bach -- Brandenburg Concerti
Handel -- Water Music [12 concerti grossi]
Vivaldi -- the 4 seasons

Classical:
Beethoven -- Symphonies #3, #5, and #9 [quartet op. 131 with Grosse Fuge), piano sonata op. #110]
Berlioz -- Symphonie Fantastique [Harold in Italy]
Brahms -- Symphony #1 [Sonata for violin and piano #1, op. 78]
Dvorak -- New World symphony ["Cypresses]
Liszt Hungarian -- Rhapsodies #1 and #2
Mozart -- Symphonies #39, #40, and #41
Rossini -- Overtures
Tchaikovsky -- Capriccio Italiene, violin concerto and symphonies #4, #5, and #6 [Piano Trio op. 50]
Rimsky-Korsakov -- Sheherazade and Capriccio Espagnole

20th century:
Bartok -- Concerto for Orchestra, violin concerto [viola concerto and piano concerto #3]
[Ernst Bloch -- quintet and Schelomo]
Georges Enescu -- Rumanian Rhapsody #1 [Sonata for violin and piano in the popular Rumanian style]
Gershwin -- centennial collection (2 CD set--really great)
Khatchaturian -- Gayane Suite [piano concerto]
Mahler -- "Resurrection" Symphony
Prokofiev -- Classical symphonie and Suite from "Love for 3 Oranges" [violin concerto #1]
[Schoenberg -- Verklarte Nacht]
Shostakovich -- Symphony #5
[Skriabin -- late piano works (op. 65 through op. 74)]
Richard Strauss -- So Sprach Zarathustra, Ein Heldenlieben, [Metamorphosen and 4 last songs]
Stravinsky -- The Firebird, The Rite of Spring [Petroushka--complete if you can find it]

I don't know if you like opera (I know I don't) but these 3 are essential (people who like opera would recommend Verdi and Wagner):
Beethoven -- Fidelio
Moussorgsky -- Boris Godunov
Gershwin -- Porgy and Bess

Brilliant, thanks.

I'll let you know how I get on.

I was going by memory, so the clerical accuracy was not so good. The Grosse Fuge goes with opus 130, not opus 131. It is a serious candidate for the title of "greatest piece of music ever written," but the first time you hear it, it might sound kind of rambling and aimless.

The Bloch quintet I had in mind was his first one--piano quintet #1 (1923)--but usually the two of them are on one CD anyway. Quintet #1 is the only piece I've heard that has quarter tones in the score and they sound good.

By pure coincidence, a quartet of 17-year-olds just played the Grosse Fuge on the radio, after talking about how they got only 2 weeks notice that they had to play it "and they were like, no way, I mean, do you believe this, it's like totally no way.

I also just listened to the Bloch quintet for the first time in years, and it's more amazing than ever, particularly at the end, when--even though the thematic material is the same as you've been hearing throughout the piece--you get a sense of all the stress and tension having been worked out and resolved.

Opera is a tough sell nowadays, and most of them probably aren't good enough to justify the effort and expense of mounting a production.

My favorite is Fidelio by Beethoven, but it's not a big favorite among opera lovers.

Fidelio was been secretly nabbed by the secret service of an unidentified police state, because he was a political reformer. His wife, Leonora, disguises herself as a guy and gets a job at the prison. Then she goes in with a pistol to get out.

The disguise is never fools me, but some Leonoras look very fetching wearing boots and holding a pistol:

Here's Fidelio singing that great aria "I Sure 'nuff got them Mean Old Prison Blaues:"

What about Tōru Takemitsu???!?!???!!

There were some names I left out just to see if anyone would notice.

Seen this opera?

I recently was at an opera in Venice. T'was okay.

All those years of voice training for all those cast members, a full orchestra in the pit, all those props and stage hands for the scene changes. It's hugely expensive and can only be done with the help of grants and scores of generous benefactors, because they could never charge enough for tickets to break even.

And after all that, my reaction to most operas is like yours: " 'Twas OK."

But there are still a few that are worth it.

And it was the Italians who invented opera. One Italian in particular--Claudio Monteverdi--invented it in 1607 (others tried to invent it a few years earlier, but failed).

The first real Opera was Monteverdi's Orpheus. I would have mentioned it, but it's way outside of the mainstream because of being so archaic.

Here's the overture and prologue, sung by the goddess of music, informing the audience that this show is going to me a musical. Check out the crazy instruments in the orchestra:



And here's Orpheus, singing about what a great gal Euridice is:

I saw Madama Butterfly a few years back. Thought it was brilliant.

Speaking of Porgy, it says here his Gullah relatives had a get-together not long ago:

http://www.charlestoncvb.com/visitors/news_article.html?id=702