Reddit mentions of Einojuhani Rautavaara: String Quintet "Unknown Heavens" / String Quartets 1 & 2 - Jean Sibelius Quartet

A few, not all of which are YouTube [YT] links.

• Bach: Golberg Variations — Murray Perahia [YT]
  
• Hindemith: Mathis der Maler — Yoel Levi & the ASO
  
• Shostakovich: String Quartet No. 8 — Kronos Quartet [YT]
  
• Dutilleux: 'Ainsi la Nuit...' — Orpheus String Quartet (This actually links to the Arditti performance, mostly because it follows the score. This is also an excellent performance. Link to Orpheus recording.) [YT]
  
• Bartok: Dance Suite, Sz. 77 — Andras Schiff
  
• Carter: Piano Sonata — Paul Jacobs
  
• Bartok/Lustoslawski: Ctos. for Orchestra — Christoph von Dohnányi and the Cleveland Orchestra
  
• Feldman: Piano and String Quartet — Kronos Quartet and Aki Takahashi [YT]
  
• Harbison: The First Four String Quartets — Lydian Quartet
  
• Rautavaara: String Quintet "Unknown Heavens" — Jean Sibelius Quartet
  
• Lassus: Prophetiae Sibyllarum — Hilliard Ensemble (Not the Hilliard performance, but you just have to hear a little of this. The Hilliard Ensemble does things with this work that are truly other-worldly... Link to their recording)
  
• Ives: Concord Sonata — Gilbert Kalish
  
  Okay, that's enough. Sorry for all the twentieth century stuff, but if I started listing off my favorite music from the 18th century I'd be typing all night. I'd rather let other folks give their suggestions for music from before 1900.