In that regard, music is something that is sometimes hard to find. Something powerful and dark is preferable to me. In that regard there is a new cd I picked up that I just knew would fit the bill.
Hans Zimmer does it again in the "The Dark Knight Rises" soundtrack. Its dark tracks include A Storm Is Coming, Despair, Fear Will Find You, and Necessary Evil. It is dark with lots of action in the music.
I highly suggest getting this soundtrack for the right feel for warhammer 40k, and if you love this one, do not forget the previous soundtrack "The Dark Knight". Finally for those that this is just not dark enough, there is one that is not for the squeamish, the two disc soundtrack to "Shutter Island" might be the right choice for you.
Anyone else have some good dark tunes that fits into the 40k universe?