About mixing guitar scales.....?

Okay. I have only 2 years of knowledge on musical education and this question bugged me since a month ago. I like to play Drop D a whole step to get that metal feeling and I always use the D melodic minor scale (ascending and descending mixed together) for that dark sound. But, since I want a less limited scale, but not a chromatic scale, what scales should I use to mix and get that Nu-Metal sound and how do I mix them together? Disturbed, for example, sounds like it's in the key of D Minor, but in the song "The Night", the one part of the riff is played a half-step over the key note. I'm quite limited in scales, so what form of minor is it in? Thanks for answering my question.