Anything by E Nomine is extremely epic-sounding.
The Itachi AMV in my sig has some pretty epic music.
Anything SOAD produces is pure fucking win.
These AMVs win:
YouTube - Deidara - The Explosive Ninja of Akatsuki
YouTube - Itachi and Kisame - Woho!
YouTube - Lord Orochimaru - Vater Unser
YouTube - Espada amv - Like Suicide
YouTube - Holy Diver - Naruto AMV
^Note: Those are not the best AMVs I've got. But they do have some of the most epic songs.