Okay seems I have time to write a small little lesson which the more metal of you would love to consume. These are very common scales so don't get all grumpy if you have heard of them or even know them.
Harmonic Minor(from major): I- II- bIII- IV- V- bVI- VII- I
(from minor): I- II- III- IV- V- VI- #VII- I
A Harmonic Minor: A- B- C- D- E- F- G#- A
C Harmonic Minor: C- D- Eb- F- G- Ab- B- C
The Harmonic minor scale has a nice little classical tone to it. The best thing to do is view it as a Natural Minor scale with an Augmented seventh. If you are using the Natural major position for it you may selectively use it like one just notice the augmented fifth. Major augmented chords I-III-#V sound good with the harmonic minor scale as long as you remember to use the relative major of the minor you are playing in... fe: CM= Am, GM=Em, DM=Bm that type thing as always.
Melodic Minor(from major): I- II- bIII- IV- V- VI- VII- I
(from minor): I- II- III- IV- V- #VI- #VII- I
A Melodic Minor: A- B- C- D- E- F#- G#- A
E Melodic Minor: E- F#- G- A- B- C#- D#- E
Yeah, I know I shouldn't even bother posting this one considering it's probably not the most conventional thing to use in metal, I guess that's why they call it the JAZZ melodic minor. Anyways, it makes for more (1 more) dom 7th and (1 more) min 7(b5) chord if you care to try it on it's a lot of fun or run through each of it's modes and you may eventually find something more suited to your style. Fight a standard find a way to use it. Just don't make me slap you for making it sound like some Trey Anastasio... Yeah, I know lame joke.
Pentatonic Minor(from minor): I- III- IV- V- VII
A Pentatonic Minor: A- C- D- E- G
E Pentatonic Minor: E- G- A- B- D
You all know this I'm sure but I try to go over everything regardless of who knows it and who doesn't know it. I guess I'm walking to my own drummer's beat. Anyways pentatonic minor is a major erm... Hick metal thing... sorry Pantera. Pantera used the pentatonic minor in many of their riffs but Dime always used it very unconventionally he loved to throw in an augmented step here and play it with an augmented step in it so I guess it wouldn't be pentatonic erm yeah duh... sorry.(notice I didn't really feel like going over it, message me if you need me to. I'm lazy at times)
If you combine the natural major and the natural minor scale together you get a nice little ten note scale. This is also a very common thing in classical music. I only hope that most of you are as classically influenced as I try to be. Anyways the formula for this nice little Mozart, Beethoven, Bach thing is.
Classical thing(from major): I- II- bIII- III- IV- V- bVI- VI- bVII- VII- I
This is how they created their complex chords and combined them so easily while staying within a common key. They felt the Seven note diatonic scales were to linear whereas the 12 tone method which Schoenberg(I think) and others pioneered was to random and lacked shape or definition. Of course by combining the parellel(same root note) major and minor you have a much broader choice of sounds in which you can use.
Each of the scales I mentioned have modes as do all scales. Each one gives a slightly different sound and of course each degree is a little different so your scale harmonies may sound awesome to you. I hope anyone who reads this thread finds a very unconventional use for the information. Please don't forget though. Music theory is more or less a basis of ideas which you can use in your playing. Never rely solely on theory, use your ears and test it. Never stop thinking for yourself. Anyways, I think that's all for now. Later.
P.S. there are many more exotic scales and I could go a lot more in depth with the chords to these few exotic scales but that is for a different time. I'm going through the basics. It helps immensely to know a bit of scale theory before stepping into chord theory. I'll even put in a little bit of things to use on the guitar such as quartal harmony... it throws people off since you use a P4-A4-P4 to create a seventh chord instead of a M3-m3-M3. Guitars/guitarists generally use tertial harmony and well quartal is just a little bit different. Anyways, sorry... if anything in my PS confuses you just don't pay any attention and I'll explain it later. I'm trying to kind of hurry through this but it does take time and make sure to let me know your thoughts.
P.P.S. I wrote this like 3 years ago, just felt I should make it accessible on UG.