Choosing five is a tough choice, but whether it be top three, top five, or top fifty, I would always place Jascha Heifetz playing both the Beethoven and the Brahms Violin Concertos on one CD, RCD 5402 as my top dog.
The next four to make a total of five are tough but I submit the following.
Beethoven Piano Concertos No. 3 & 4 by Murray Perahia and Bernard Haitink and the Cocertgebouw Orchestra CBS MK 39814 or Beethoven Piano Concerto No. 5, again with Murray Perahia and the same conductor and orchestra, CBS MK 42330.
Yo-Yo Ma, Great Cello Concertos (Dvorak * Elgar * Haydn * Saint-Saint * Schumann on two CD's CBS M2K 44562. If you're anxious or curious to hear Jacqueline du Pre play these same pieces, you can opt for her versions on EMI.
Brahms 4 Symphonies, Leonard Bernstein with the Vienna Philharmonic on 4 CD's DGG 415 570-2.
ARIA A Passion For Opera is a great compilation of famous arias sung by the best of the opera stars. It will whet your apetite into learning more about opera and delving deeper into the passion of listening to opera.
You will become an afficionado of the classics after listening to these starters. There is so much to enjoy. listening to the same pieces but with different performers will bring more joy as well as develop you into a critic, perhaps the hightest brow member of your crowd. How's that for a pun.
Happy listening.