To me, the great Klemperers are:
Mahler: 2 and 9 (a devastating first movement, imho, the single greatest thing K ever put on record), Das Lied (the next greatest thing K ever did). I pretty much agree that Klemperer's studio recordings are all worth hearing at least once. And that does include the Mahler 7--you simply have to hear it to believe it was ever made....some of the oddest tempo choices I have ever heard.
Dvorak: New World Sym --very powerful
Berlioz: Sym Fantastique --amazing clarity and drama--plus a Gluck "Iphigenie en Aulide" overture that will blow your mind
Bruckner: 4-9, they are all good, especially a beauiful 7, and I welcome edits in the finale of 8
Brahms: I like all 4 Syms by him, plus overtures, etc, Violin Concerto, German Requiem (a GREAT recording)
Mozart: the late symphonies (I have not heard the Haydns), Magic Flute, Overtures with Masonic Funeral
Beethoven: Fidelio, Symphonies, Overtures (a stunning collection CD of those), Violin Concerto
Romantic Overtures: Weber (3), Humperdinck, and Klemp's own "Merry Waltz" --solid performances
Mendelssohn: Sym 3 & 4, Midsummer Night's Dream --not the infamous "brontosaurian romp" it's made out to be
Schubert; Sym 5 & 8
Schumann: Syms 1-4, Manfred Overture
Wagner: Flying Dutchman, orch music collections--all great. (If only he had recorded Parsifal...)
Baroque composer recording are worth hearing, but none really satisfies me, and performance practice has surpassed them