Basically every song in the entire Silent Hill series deserve a spot on this list. Just search up Silent Hill OST on youtube. Or you could just find some convenient playlists on "stripedlady's channel."
There's really too many to count. Silent Hill is full of these.
One more, Betrayal from Silent Hill 2. It's the perfect music for a final battle with a demon monster from Hell. It's so dark and depressing but awesome at the same time.
Don't forget the song in the opening of Silent Hill 3. If you listen to it, watch the scenes for it too.
Hometown the end credits theme from Silent Hill 3. The original theme from the first game (which, itself, totally deserves to be on this page), remixed, with lyrics sung by Joe Romersa? Hellyes.
The creepy-but-beautiful Music Box theme from Silent Hill 2. A very sad piece.
I can't believe i'm the first person to mention Not Tomorrow, the song that plays during Lisa's reveal in the first game. It's just so haunting and melancholy.
This may seem a bit weird, but there seems to be something very addicting about Mira's Theme, the piece made entirely of barks and growls played during the dog ending. Catchy? Very...
And finally someone gets around to mentioning True. Notable in large part for playing during The Reveal in Silent Hill 2, it's devastating in any context. Its inspiration, Tears Of... from the first game, is also quite good.
Alex's Theme from Homecoming is a beautifully haunting piece of music.
"Esperadote", the theme song to the worst ending in the first game. It's a downright gorgeous, operatic theme, sex to your ears. Unusually for a Silent Hill game, the lyrics are in Spanish.