Gregorian chant is awesome. Saya-kun is a weeaboo and also likes Organum. CHOOSE A SIDE.
Gregorian chant is the original. Organum lead directly to Polyphony, which is kind of a big deal. Use wikipedia if want to actually learn about this stuff.
Its not metal. Really. It was requested in IRC so here it is. This is also proof that stuff you request in IRC will get here.
Monks of Silos (Gregorian Chant) Here
Marcel Pérès: Ensemble Organum (That silly Organum crap) (Its FLAC and huge)
Part 1 Part 2 Part 3