Well, obviously the obvious - the Beethoven, the Brahms, the Tchaikovsky - technically and artistically just wonderful.
Bartok's first - the raw emotion of unrequited love/lust is very apparent!
Schoenberg's is interesting. Bruch's first and the Scottish Fantasy. Mozart's Sinfonia concertante.
Mendelssohn's in e. Dvorak's in a.
. . . but there are so many really fine works - Hindemith, Shostakovich, Bacewicz, Spohr, ....
Of course, Bach and Vivaldi wrote magnificent "concertos" but the Baroque's definition of concerto is somewhat different than what it came to be accepted as.
... and Berg's and Schumann's and Prokofiev's and and and ...