Anything from the Bioshock soundtrack or Bioshock 2 soundtrack.

Gary Schyman nailed the "creepy-without-random-screams" in both soundtracks, which helped make both games perfect, in my opinion.

The soundtrack from the first game is actually available for free (LEGALLY, it was distributed online by the developers).

The soundtrack for the second was actually released as an album labeled "Sounds from the Lighthouse", though I'm not sure its regularly available. Youtube has some of it, and there's one video with the entire track. I personally like it better than the soundtrack released from the first game, but its harder to find.