Many good suggestions. I would start with a cross-section of great composers and genres until you figure out what you like. From the above list (mostly). . .
Concerto for solo instrument and orchestra
Tchaikovsky’s violin concerto in D.
Mozart's Piano Concertos, from #18 on up, esp. nos. 21-26,
Rachmaninoff Piano Concerto 2.
Large scale works for orchestra
Beethoven's 9th Symphony
Mussorgsky Pictures At An Exhibition
Smaller scale works for orchestra or for ensemble
Vivaldi The Four Seasons
Brahms Clarinet Quintet
Solo instrument
Bach's Sonatas and Partitas for Solo Violin
Shostakovich's 24 Etudes and Fugues for Piano
Concerto for solo instrument and orchestra
Tchaikovsky’s violin concerto in D.
Mozart's Piano Concertos, from #18 on up, esp. nos. 21-26,
Rachmaninoff Piano Concerto 2.
Large scale works for orchestra
Beethoven's 9th Symphony
Mussorgsky Pictures At An Exhibition
Smaller scale works for orchestra or for ensemble
Vivaldi The Four Seasons
Brahms Clarinet Quintet
Solo instrument
Bach's Sonatas and Partitas for Solo Violin
Shostakovich's 24 Etudes and Fugues for Piano