Some of the pieces above really don’t answer the question that was asked.
Mahlerian’s list was a good answer. Limiting it to 18th- and rhythmic early-19th century works, I’ll complement it with:
Vivaldi: The Four Seasons (technically 4 pieces but they are short)
Bach: Cello Suites, pick one or all
Bach: Brandenburg Concerto No. 5 (or all of them)
Bach: Mass in B Minor
Haydn: Symphony No. 94 “Surprise”
Mozart: Symphony No. 41 “Jupiter”
Mozart: Piano Concerto No. 20
Mozart: Serenade “Eine Kleine Nachtmusik”
Mozart: Magic Flute
Beethoven: Symphony No. 5
Beethoven: Symphony No. 7
Beethoven: Piano Sonata No. 32
Some of which I rarely listen to — I debated over “Eine Kleine Nachtmusik” but I wanted to include some chamber music, and it is definitely one that everyone knows. The Haydn String Quartets are a fount of quality, but I don’t know if any individual one is so famous.
I started to add another list going further into the 19th century, but I know you’re already deluged with suggestions.
I second Mahlerian’s suggestion to listen to complete works, not just the most-famous bits. And youtube is okay for exploring, but you might find it worthwhile to subscribe to spotify or some other streaming service. (You can listen to spotify for free, but you have to pay to get rid of the ads.)