This could be a long list, but I'll mention only the ones that come immediately to mind: Miles Davis's album "Kind of Blue"; Bill Evans & Jim Hall's album "Undercurrent"; several cuts from Art Pepper's album "Shoes of the Fisherman"; Sibelius's "Swan of Tuonela"; duets from Puccini's "La Boheme"; Mozart's "Requiem"; Barber's "Adagio for Strings" (used as death theme in movie "The Elephant Man").
