I know exactly what your talking about, try the song Lilium from Elfen Lied - http://www.youtube.com/watch?v=RaV6eDvgiG4
or you could try Mozarts Requiem, which is probably one of the darkest songs ever written, considering he died while composing this funeral mass. Its almost like it was forshadowing his death the whole time.
http://www.youtube.com/watch?v=tcIqZoxV0sA
Lacrimosa (most known) - http://www.youtube.com/watch?v=k1-TrAvp_xs
and if you have the patience, you should listen to The Romeo and Juliet Fantasy Overture, its the retelling of romeo and juliet in music, its really foreshadowing and dark, but the love theme is really famous
part 1 http://www.youtube.com/watch?v=t-hvNB0GBDE
part 2 http://www.youtube.com/watch?v=wLTjdnZczB0&feature=related
also try some of the stuff from silent hill, the music in that is amazing
http://www.youtube.com/watch?v=nd8rBt0OUQQ
http://www.youtube.com/watch?v=PMvOkUMPZ0g
hope this helped!