Long Live Metal!!
First and foremost: Emilie Autumn is really awesome. She's not metal but her music is really inspirational and it's still got a definite edge to it. If you're interested, contact me.
Second, Powerwolf is epic win.
Folk Metal: Skyclad, Korpiklaani, Finntroll, Ensiferum, Eluveitie (early), Suidakra, Cruachan, Arkona, Kalevala, Satana Kozel, Nevid, Temnozor.
Death Metal: Vader, Morbid Angel, Death, Possessed, Atheist, The Faceless, Arsis, Fleshgod Apocalypse. Nile FTW!!!! Death!
Black Metal: Abigail Williams, Limbonic Art, Obsidian Gate, Bishop of Hexen, Sirius, Carach Angren, Bal-Sagoth, Emperor, Summoning, Deathspell Omega, Transcending Bizarre?, Arcturus (early), Sigh.
Black/Folk: Melechesh, Windir, Vintersorg
The Meads of Asphodel are highly interesting and very creative but very anti-Christian.
Doom Metal: Saint Vitus, Pentagram, Orange Goblin, Electric Wizard, High on Fire, Crowbar, Eyehategod.
Celtic: Flogging Molly, The Pogues, Dropkick Murphys, Lunasa.