Winterdome is my personal favorite out of metal bands that use violins. These folks from Hannover, Germany have the most innovative violin parts I have ever heard in metal! Their music is a combination of folk metal and doom metal, featuring grunting vocals and narration, all in German. They feature an acoustic violin, which is played live as well as in the studio by violinist Lisa Hinnersmann. Although they are a folk metal band, I feel like their violin parts are really unique, as they aren't overtly folky but have more of a graceful and flowing feel to them. The violin plays a very prominent role in their music, and I feel like Winterdome was not just a metal band that decided to throw a violin in there as an afterthought, but they must have intended for the violin to play an integral part in their music.
Their latest album, Weltendammerung, has 2 discs: one is a storybook featuring narration between songs, and the other has only songs on it.
Unfortunately, I don't think this band is active anymore. Nonetheless, Weltendammerung is a real gem for anyone into violin metal.
Their album is definitely a worthwhile investment, and they are not a very well-known band either so if you like them, please support them, and tell your friends about them!
Official website: http://www.winterdome.de/
Recommended Songs: "Land der Nacht," "Ein Stiller Schrei," "Weltendammerung"
One of their songs (recommended: listen @ 480p):