I'll try to stick the most popular ones......Some are available in both full version and highlights versions.
Bizet's "Carmen"..Callas, Gedda; Paris Opera/Pretre...or:
Johnson, Domingo; Concert version..Radio France/Maazel.
Mozart's "Magic Flute"..Gedda, Popp, Philharmonia/Klemperer..or:
Schreier, Moser; Bavarian State Opera/Sawallisch
Mozart's "Marriage of Figaro"..Ramey, Te Kanawa, Popp, Von Stade; London Philharmonic/Solti
Mozart's "Don Giovanni"..Battle, Ramey, etal; Berlin/Von Karajan
Puccini's "La Boheme"..Freni, Pavarotti; Berlin/Von Karajan
Verdi's "Aida"..Freni, Carreras; Vienna State Opera/Von Karajan
Gershwin's "Porgy and Bess"..White, Haymon; London Philharmonic/Simon Rattle
Available as a set, because both operas are short and usually performed together are Mascagni's "Cavalleria Rusticana" and Leoncavallo's "Pagliacci"....Pavarotti, etal; National Philharmonic/Giuseppe Patane;
In Rusticana you will notice that the music at the midpoint was used as the theme music in the movie "Raging Bull".
You may also look for Verdi Highlights with samples of the Operas "Aida", "Otello", "Rigoletto", and "La Traviata", "Il Trovatore" and more. There is a good one on Polygram; catalog number 469217