Several that came to mind have already been mentioned, but I don't think anyone's mentioned The Devil...
https://youtu.be/O9UBeFG6grohttps://youtu.be/sKJzKWqvHakI second (or third or fourth) Bridal Mask, Missing Noir M, Arang and the Magistrate, and yeah, that theme song for Legend is pretty epic too. :) A good score without too much emphasis on sappy ballads or pop music where it doesn't fit perfectly is my ideal drama soundtrack.
There are some songs on the Late Night Restaurant (kdrama) and Signal soundtracks that I like a lot too (with vocals, even). Just a bit different from the standard pop and ballad-heavy soundtracks that we usually get.