Orf, Wagner, Basil Poledouris, and Sergei Sergeyevich Prokofiev, among others. I like all types of Classical music, but especially those that are bombastic, one might even say 'pagan', anthems. It really goes against the widespread perception that orchestral music is some how more meek or retired than modern forms. I would rank Orf's 'O Fortuna Imperatrix Mundi' up there in sheer 'heaviness' with any heavy metal. The blending of the two genres in some Scandinavian artists like Tarja Turunen shows how much they drink of the same inspiration and vibe. Just check out Nightwish's 'Ghost Love Score'. Very powerful stuff!
By way of example http://www.youtube.com/watch?v=OEAgchvPcc8