Historical:
Schnabel's and Weingartner's Beethoven, Bruno Walter's live Fidelio and Don Giovanni (although neither has good sound), Heifetz/Feuermann Brahms double concerto, Heifetz/Toscanini Beethoven concerto + Heifetz/Koussevitzky Brahms concerto
Non-historical
Bartok: Early chamber music with Jando etc. Violin sonatas with Pauk/Jando
Brahms: 4 hand piano series (Frankly, I care only about the "original" works but they are all interesting and done very well - plus I met Christian Köhn several times socially and he is a very agreeable person..)
Buxtehude: Harpsichord music with Wilson, Chamber music with Mortensen and friends (supposedly the discs with Mortensen solo are also good as well as some of the organ and vocal series but I have not heard them)
Dohnanyi: Sextet + Senerade, fantastic music and great recording
Dvorak: string quartets and other chamber music with the Vlach quartet, great for filling gaps and pretty good anyway, if not up with the best recordings by the Smetana, Janacek or the old Vlach and other vintage Czech ensembles
Wind serenade (Oslo), recommended above, very nice disc, maybe even more for the less frequently recorded fillers (Enescu + Janacek)
Franck: piano quintet Levinas/Ludwig
Haydn: The Kodaly quartet series and some of the symphony series are quite and and certainly good enough as fillers, but I was not really impressed by any of them, that is one can usually do considerably better. Exception maybe for the "op.3" which is not by Haydn and therefore not included in most recent recordings; they do a very good job.
Liszt: Arnaldo Cohen with Totentanz etc.
Monteverdi: Madrigals
Mozart: Piano quartets
Reger: Chamber works, if one cares about that stuff
Rossini: Tancredi, Podles Alto arias recital
Shostakovich: 24 Preludes+Fugues and another disk with Sherbakov, Piano quintet + Schnittke, what I have heard of the string quartets is quite good but there are now so many cheap great complete recordings of them, one can probably do better even cheaper
Spohr: Clarinet concertos
Stravinsky: I have two or three of the Craft recordings; very good for lesser known works (and maybe for others, too)
Weber: Symphonies and piano concertos (although one can probably do somewhat better, the fillers of the symphony disc are hard to come by otherwise)
I guess there is a lot more that is at least pretty good and even more I never heard and never will.
