Rachmaninoff's piano concertos are usually pretty good (a shame that he was quite anti-communist).

Sibelius's Violin Concerto and D minor (his opus 47) is pretty good as well.

Scarlatti's Sonatas have also been great every time I've listened to one of 'em.

Gustav Mahler's Symphony No. 5 is also a favorite.

You may have noticed that these songs aren't household names (like "the well-tempered clavier" or the "moonlight sonata") but I'm trying to avoid those for now.

Also, not a composition highlight, but shout-out to Ryuichi Sakamoto.

What are your favorite compositions/symphonies/sonatas/etc. of classical music in general? Can range from anywhere to early baroque to the Soviet composers to the 21st century and so on and so forth.