Iron Maiden: Phantom of the Opera, Aces High (of course), Hallowed be thy name, or Revelations. My favorite lyric in any song is from Revelations, it is when I first realized these guys were actually intelligent guys not just a bunch of headbangers.
"Oh god of earth and alter, bow down and hear our cries
Our earthly rulers falter, our people drift and die
The walls of gold entomb us, the swords of scorn divide
Take not thy thunder from us, take away our pride".
If I was a UFC Fighter choosing my "walkout" music, it would 100% be Metallica's "For whom the bell tolls"