My favorites:
Mahler-Symphony #1
Respighi-The Pines of Rome
Brahms-Variations on a Theme of Haydn
Bach-Brandburg Concerto #2 played by Maurice Andre or Rolf Smedvig
BTW-has anyone ever heard Pendrecki's "Threnody for the Victims of Hiroshima"? It's not something you would sit down to listen to to relax, but it's "interesting".
Yes, Penderecki is a great talent. I actually really like his symphonies, especially the First, the Third, and the Seven Gates of Jerusalem. Once he dropped his experimental radicalism, he turned out to be a neo-Romantic of genius. He has kept his sonorous soundscapes but produced actual music that you can "sit down and listen to."