The 3rd and the Mortal, from Norway.
When Nightwish started out, they were influenced by them, and the Gathering, mainly.
I would describe it as TG meets movie soundtrack music. It is really quiet and peaceful, that's the movie soundtrack side of it, if you know what I mean.
Their 1994 album Tears Laid in Earth is really, really good. It's only hard to download, and it'll be almost impossible to buy it. I would surely recommend it especially when you like the softer side of TG.
Especially the beginning of this song is heavy for 3rd and the Mortal terms:
http://www.youtube.com/watch?v=nNAjQPAlqBE