Ok, this idea is pretty simple and somewhat recycled. Think of any character, and then try to pick the music that would best fit them making an entrance. Let me set it up for you. You are staring at a black empty space. You hear ______________ start to play, then out of the darkness after the intro emerges_______________. Here are a few of my ideas.
Monkey D. Dragon: Rock You Like a Hurricane by The Scorpions.
Donquixote Doflamingo: The Devil's Rejects by Rob Zombie.
Roronoa Zoro: Dance with the Devil by Breaking Benjamin.
Nami: Money by Pink Floyd.
Enel: Thunderstruck by AC/DC.
Pell (in full falcon form): Dangerzone by Kenny Loggins (it's a Top Gun joke).
Portgas D. Ace: I Fought the Law by The Clash (bad taste intended).
Iceburg, Kokoro, Chimney, and the whole Water 7 lot: Crazy Train by Ozzy Osbourne.
Edward Newgate: Viva la Vida by Coldplay.
Mr. 5: Electric Worry by Clutch.
Gekko Moriah: Oogie Boogie's Song from The Nightmare Before Christmas (I personally think it's giving him too much credit, but I couldn't think of anything else).
Monkey D. Luffy: It's My Life by Bon Jovi.
Nico Robin/Olvia: Turn the Page by either Bob Seger or Metallica.
Oars (Jr.): Monster by The Automatic Automatic.
So those are mine. Let's see what you can come up with.