Gregorian chant, it's a type of music usually sung by monks but it often finds it's way into modern music too. A band called Enigma used it pretty famously in the 90s. I know there are other more recent ones, but I forget.

Here is the music in the new trailer:
https://youtu.be/TGFZ6RJqTWY?t=1m26s

But anyway, I think it's pretty great. It goes well with the opening song and makes the dragons seem ominous, old and scary. After all Gregorian chant is a pretty ancient music form:
https://en.wikipedia.org/wiki/Gregorian_chant

Here is a more modern example of the style:
https://www.youtube.com/watch?v=TF4Orx0765Q

How'd you all like the new music in the trailer?