Edit
repare for lots of tracks I've added.
I can't really listen to the music right now, my audio driver gave out, and I can't name any names off the top of my head, but the one that plays in the Archives is creepy (which I believe is also in the chancel ^ edit, nope. 07_amb), the one that plays late in the game that plays during the beginning of Justine is cool(edit: 25_amb), and the idle theme for the Suitors is pretty creepy, if that counts. Oh, and the eerie "aaAAAHHHH" sounding music in the Library of Justine is creepy, too. (edit: 21_amb)
Edit: Finally installed a correctly working sound driver (m.bisonyes) and I checked over. Also, I didn't remember this one, but it's really creepy, and probably one of my favorites, event_darkness. The one that's used alot in the sewers and in Basile's Basement. event_brute (the morgue one) is one of my favorites too, and here's a list of ones that I don't exactly remember the origin:
02_amb_strange- I got organsms. cwhtididthere. 10_amb, it feels safe, and sorta cozy and homey. lolnope, closet time. 22_amb, it has an eerie feel, the bouncy sounding sounds are creepy too. I've only remembered it as the Justine menu theme. 23_amb02, the off chordey sounds just creep me out.