this could have been posted in the unmoderated forum. why dedicate a whole thread to something you allegedly don't care for, being random and all that?
Well, if the greatest ninja movie of all time, "Rage of Ninja", is any indication, they listen to a lot of 4-AD music, oddly enough. EDIT: the trailer on Youtube, featuring "A day" by Clan of Xymox: http://www.youtube.com/watch?v=nxCAPMzPZ-Q "I WAS SO CLOSE TO BECOMING... THE ULTIMATE NINJA!!"
I was thinking Metal. Or Maybe tool, I can see Ninjas Sneaking around listening to Parabola or blasting a Dream Theater song to disorient and take out an entire army.
I think Wu Tang is the only rap allowed by the code of the Ninja http://www.youtube.com/watch?v=gN2zcLBr_VM&feature=player_embedded