I have a mod that lets me play music/sound effects over the majority of the stuff in the game so besides a lot of the music that I have enjoyed (like ICC gunship, some town themes and most of Pandaria) I replaced most of the music with stuff from other games and random shit. Most of the time it doesn't even really fit the theme, but I still find it hilarious like one time I replaced the music when I would enter a battle with the recording of the naked bed room fight scene from Borat and the theme music from The Price is Right for Silvermoon.
For example I have this playing when my character is running back as a ghost.