Basic stuff - classic recordings, one each composer and this is just what popped into my mind. No consideration for "HIP" performances, just good singing and conducting. Listed by composer, title, conductor and label.
Beethoven - Fidelio - Klemperer - EMI
Berg - Wozzeck - Abbado - DG
Debussy - Pelleas et Melisande - Abbado - DG
Mozart - Le Nozze di Figaro - Kleiber - Decca
Puccini - Tosca - De Sabata - EMI or La Boheme - Beecham - EMI
Ravel - L'Enfant et les Sortileges/L'Heure Espagnole - (a 2fer) - Maazel - DG
Strauss - Salome - Karajan - EMI
Verdi - Otello - Serafin - RCA Living Stereo
Wagner - Die Meistersinger von Nurnberg - Karajan - EMI
Weber - Der Freischutz - Kleiber - DG
and I will add one "highlights" disc:
Strauss - scenes from Elektra and Salome - Reiner - RCA Living Stereo
I'm sure I'll think of omissions later.