I'm searching for sort of a powerful epic battle feel, similar to those that influence Norwegian Black Metal bands like Dimmu Borgir, etc. Probably a pretty far out question for a general "rock" category, but I have no idea where to start.

Start with Wagner and Stravinsky

links here

http://www.songofthesalesman.co.uk/ad.aspx?partist=Wagner

plus Mussorgsy's Night On Bare Mountain

http://www.songofthesalesman.co.uk/ad.aspx?partist=Mussorgsky