Beethoven's Equali are exceedingly duff, are they not?
Oh, I dunno... to me they have a kind of spare elegance and nobility as funereal music, although you'd barely guess whose work they were :) Trombonists are almost always glad to have something actually written for their instrument by a serious composer (ie not Glazunov).
I don't know Dussek's music well, probably because I'm a weak pianist - but I like what I've heard. Spohr, Cherubini, Marschner and Mayr are other names worth exploring in the opera field. I suppose we should properly include the omnipresent Salieri, too :)