The great symphonies of Mozart,Haydn,Beethoven,Schubert,Schumann, Mendelssohn,Brahms,Dvorak,Tchaikovsky, etc are staples of the repertoire and have been recorded countless times,but there are some less familiar symphonies people should get to know if they are already familiar with the basics.
For example: The first six symphonies of Dvorak,which are rarely performed ,and are
chock full of meloic invention and radiant lyricism. The New World and nos 7 and 8 are very familiar, but no one who loves them should miss the first six. There are excelent recordings by Rafael Kubelik, Istvan Kertesz,Witold Rowici, Libor Pesek,Vaclav Neumann and others.
Paul Dukas: Symphony in C: There's more to this composer of the Sorcerer's Apprentice than you might realize. His one surviving symphony will make you wonder where it's been all your life.
Mly Balakirev: (1837-1910). Balakirev was one of the most important and influential figures in 19th century Russian music, but for some reason,his music never achieved the fame of the works of Tchaikovsky,Rimsky-Korsakov,Mussorgsky and Borodin.
Try his melodious symphony no 1 in C. It has both the flavor of Russian folk music and the exotic non-russian parts of the former Soviet Union. You'll love it. This composer died 100 years ago. Why isn't his music receiving more attention?
Franz Berwald (1796-1868). Berwald is probably the best known composer of Sweden. His highly original and quirky music has had a fair number of recordings, but you almost never hear his music live. What a pity. It's somewhat like Mendelssohn, but much quirkier and unpredicatble.
His four symphonies have been recorded by Neeme Jarvi, Herbert Blomsted,Okko Kamu, and other conductors. Berwald's music sparkles!
Albert Roussel: This great French composer,who lived from 1869 to 1937, has unfortunately been
overshadowed by his contemporaries Debussy and Ravel. But he was his own man, and wasn't really an impressionist at all, although his music is very colorful.
He wrote four symphonies, of which the best known is the third, but all are very much worth hearing.
His music is much more vigorous, earthy and straightforward than Debussy anbd Ravel's, and full of pounding rhythms and pungent harmonies.
Try the recordings by Stephane Deneve on Naxos, or those of Yan Pacal Tortelier and Neeme Jarvi on Chandos, or Marek Janowski and Charles Dutoit.
Wilhelm Stenhammar: This fine Swedish composer lived from 1871 to 1928 and has sometimes been called the "Swedish Brahms". His music is melodious and beautifully crafted .
His two symphonies are gorgeous. Try the recordings of Neeme Jarvi.
Franz Schmidt: This Austrian composer lived from 1874 to 1939, and wrote music in a ripe late romantic style of his own. He studied with Bruckner as a young man.
His four symphonies are also gorgeous . There is a complete set on Chandos with Jarvi.
This is just the tip of the iceberg folks. There's a lot more to explore.