It is hard to think about Dark Vader and the Galactic Empire without having that "Imperial March" tune pop into your head. What theme songs might you apply to different Warhammer 40,000 armies? Tchaikovsky's "1812 Oveture" for the Valhallans? Some kind of heavy metal for the Necrons? Maybe "Wham!" or "Culture Club" for certain Elder craftworlds? What are the 40k top 40?