The newest thing I've discovered is 20th Century Classical and avant-garde Classical. Love the stuff. There is some amazingly fucked-up stuff there. My Music has just bought a CD of it for me and the department at school. These guys were weird decades before the members of Meshuggah and Gorguts were even born.
One of the great landmarks of this era was the invention of atonality by Arnold Schoenberg. He was the first to go mad and defy melody. Death metal must nod its head to him.
Basically, in atonality, you forget using the minor/major keys or scales and use all 12 notes. After writing some works in a very raw atonal style, most famously Erwartung (1900-ish), which shocked its audiences in performances, Schoenberg disappeared for 11 years to devise a new compositional system for atonal music, called serialism or dodecaphonics, which allows it sound ordered and grounded despite its wild nature. It's an absolutely fascinating way to write, especially for the tech-metal heads out there.
Thus I will lay down the basics.
The composer, when he begins, takes all twelve chromatic notes and arranges them into an order that pleases him. There are around 479 000 000 possibilities (I found the exact figure in an encyclopedia, John Mansley, you could probably calculate it, it something do to with factorials probably), so don't worry too much about accidentally nabbing an already written one, especially with the complexity of rhythm and counterpoint some of the guys like Boulez and Webern used them in.
This order is called your 'note-row'. You must stick to the order of notes you create throughout your piece, and are not allowed to go back to it until you have played the other eleven, although you can play the note any number of times you want before going on to the next. And you can change to other note-rows. I think you are also allowed to have note-rows of less than twleve as your piece gets on. I've seen it in some pieces.
Then certain ways of manipulating it can be employed.
Octave dispersal is popular, and makes the row sound active and jaggy. You can play the notes in any octave, so long as it is that pitch.
Retrograde is allowed, or when you play through your row backwards.
Inversion is allowed, when you play it 'upside-down'. All the intervals go the other way, ascending a perfect fourth becomes DEscending a perfect fourth etc.
Or retrograde inversion.
Transposition is allowed.
Chording is also allowed on how many notes you want, although they must be in order. So you can play the first note, then second, then the third and fourth in a chord, then must follow the fifth, for example.
You are also allowed to change the dynamics and durations of your rows' notes when you repeat it, just so long as that order of notes remains.
Learning to improvise in this style can be difficult, but it is excellent practice, better for coordination than learning your scales, I say, and a very creative way of getting to grips with alternative sounds and melodies.
The advanced composers among you may be further interested in total serialism, where counterpoint is introduced through the use of more than one note-row at once.
The Piano Sonattas, particularly No. 2 and No. 3 by Pierre Boulez are good reference. Try digging around Myspace. And I do warn, it's MAY be quite hard to stomach for even the hardened of ear.
Hope it's of use, Callum.