For ourselves? I, like our forum member the Crusher who does it in real life, would walk out to 'The Crusher' the Ramones song. They have a lot of great walk out tunes that would pump up a fighter and/or the crowd. If you are fighting Anderson Silva or something, they have 'I Believe in Miracles', and after that fight when you are trying to start a comeback you could go with 'Strength to Endure', and there is always 'Beat on the Brat' when you're fighting your least favorite opponent.
Nobody F's with the Jesus
(Sig by Killz)