here's a couple of carefully selected top recommendations from my modest collection - which is now something like 3 months of continuous music - CD review each saturday morning on radio 3 is usually a expensive listen
Absolute favourites: Schubert's 9th, Stravinsky Rite of Spring, Bach St John's passion, though hundreds of other contenders
Schubert 9th - 60 mines of utter perfection. There are some dud versions, my favourite is Boult Royal Phil live - the best of my 6 or 7 versions of my favourite symphony - and the reason I took up the French horn (amateur of marginal talent re-starting after 30 year gap). Schubert should swing - not all versions do - and "it don't mean a thing if it ain't got that swing" as a later musician put it.
Bach - St John's Passion - 3 CDs worth of perhaps the finest music ever written. John Elliot Gardner box set of this and the St Mathew and much else is a strong recommendation.
Stravinsky rite of spring - definitely a piece that like Beethoven's 3rd changed music for ever - I've got lots of good versions: Bernstein, Markevitch, or Stravinsky himself
More widely:
At the risk of heresy I've not got a great love of Mozart - other than the requiem, but as a horn player got to give a plug to Tony Halstead's version of the horn concertos which is a bit special. Magic Flute is great live though.
Beethoven - for anyone's top 10 symphonies list, Beethoven would have several slots: 3rd and 9th changed the language of music, and the 7th is a perfect masterpiece.
Rather neglected Mendleson is perhaps next. All his considerable output is fabulous stuff - astonishingly so for stuff he wrote as a teenager.
I'm not so fussed by late romantic music, though Mahler (5th &7th), and some Richard Strauss would be worth exploring. (Don Juan, Till Eulenspiegel, also Sprach Zarathustra, and both horn concertos)
then you get the start of "modern" music - Vaughan Williams, Sibelius, and perhaps Debussy, Poulenc, shostakovitch (check out 5th, 10th particularly) who take a different direction to lush romanticism.
Then stravinsky - the most important 20th century composer perhaps?
Perhaps not.for everyone but I do find myself listening to some real "modern" music, Schoenberg Pierre Lunaire (either / both of Jane Manning's version). lots to explore - but more an intellectual pursuit than a sing-along.
And now Phillip.Glass and John Adams writing accessible, melodic, operas on important themes.
Very very Early music - Kassia & Hildegard of Bignen - some of the earliest ever written music. And still being played 12 later centuries for Kassia !
Somewhat early music - anything recorded by the Tallis Scholars -probably the best singers on the planet. So much to choose from Byrd, Tallis, Pallastrina and Josquin's Missa Pangua Lingua a particular favourite.
Pretty much Anything with Emma Kirkby in it is another good bet for early music.
I could go on... and on..
Going to be a slow trawl through all of these, I think - wonderful 
