Xenakis:
http://www.youtube.com/watch?v=bGZyn4UiB6cChopin's "Funeral March", from Piano Sonata No. 2, and Berlioz' "March to the Scaffold" from Symphonie Fantastique
Iancu Dumitrescu is more contemporary and along remotely similar lines. I have several discs by him (and Ana-Maria Avram), and they're all high quality, interesting, powerful works. He's about as consistent as I've found. Minimalist density. One of those who gives the old hi-fi a workout. I think #1003 was my introduction to them. Reminds me of a classical composer riding the rails with David Jackman.
György Ligeti
Sofia Gubaidulina
Franz Schubert managed composing some really sombre & brooding Lieder, like "Doppelgänger" -
http://www.youtube.com/watch?v=fKVnL9JvuO8 (the Pestdemon tape Doppelgänger is of course more than slightly inspired by this piece).
Chopin's prelude in C minor, which you all know from a certain Italian movie:
http://www.youtube.com/watch?v=c97Lsxyo ... re=related (played by some guy, not recording)
Surprised no-one's mentioned Alfred Schnittke & his Requiem. His drifting in and out between minor and major tonality really messes with your ears, very dubious...
http://www.youtube.com/watch?v=GqdB3WU_CXIhttp://www.youtube.com/watch?v=75Dqh5PWbWo - Credo, with a nice drum beat. The deeply religious do it best.
Shostakovich, only getting bleaker and bleaker as the years progressed in Soviet until the '70s. This one is pretty classic, but still very doomy, far from uplifting..!
http://www.youtube.com/watch?v=gSoKpCXW ... re=relatedSome of his symphonies are rather heavy as well, I think no.7 ("Leningrad Symphony"), second or third movement, very war-like with this menacing snare ostinato...
Krzysztof Penderecki: This is heavy as hell & same composer for THE EXORCIST and THE SHINING:
http://www.youtube.com/watch?v=fwaEOyOw ... re=relatedhttp://www.youtube.com/watch?v=WAdZr6OQ ... re=related from THE EXORCIST soundtrack (I can't find an easy free d/l for complete sndtrk):
http://www.youtube.com/watch?v=kE_Y78TH ... re=relatedhttp://www.youtube.com/watch?v=lcRYdPgt ... re=relatedBela Bartok:
http://www.youtube.com/watch?v=WAdZr6OQ ... re=relatedHugues Dufourt's "Saturne", for orchestra and electronics.
http://www.sequenza21.com/sudol/?p=300Hugues Dufourt "LäAfrique et LäAsie d'apres Tiepolo"
Gustav Holst - The Planets - Mars, the Bringer of War
http://www.youtube.com/watch?v=L0bcRCCg01IAllan Pettersson's 6 & 7th symphonies are worth mentioning