The first reply to this forum suggested playing a major scale and flattening the 6th - this is a harmonic Major scale not a harmonic minor (for which you sharpen the 5th and start on the 6th), they're both great scales and well worth playing with.

Here's another really cool scale for very evil music;

BCD#EFG#AB

i.e. a harmonic minor with a sharpened 4th. This outlines the following chords; A minor, C augmented, E major, F major, F minor.
The shapes are really easy to finger too.

The hungarian Major scale is another really nasty one! Try A Harmonic Minor (ABCDEFG#A) and then flatten the E.

YOu can get modes of Melodic minors two ways; sharpen the root note of a major, or flatten the 3rd of a major. This way you can move around the circles of 4 and 5 a new way too

e.g. C major, C melodic minor (CDEbFGABC), Bb Major BbCDEbFGABb
or
C major, DMelodic Minor (DEFGABC#D), D major DEF#GABC#

This is too hard for me to get my head round at the moment but you may want to see what you can do with it.

As for chords I love Sus 4s - all you do is get a major or minor triad, kill the 3rd (i.e, the major/ minor character) and play a 4th instead. The close interval between the 4th and 5th gives a nice jazzy feel to your progressions. They're simple enough to not sound too clangy with overdrive too but they're pretty aggressive.

I have a music theory page at my brother's site at http:\\www.classaxe.com
If you just look under "friends", click on Andrew F. and follow leads to my music theory site.