Answer:
Well, you didn’t exactly specify if it was to be from TV, film, or games, so I thought I would give my top 3 (mostly because they’re all favorites and I can’t decide).
The opening sequence of Resident Evil by Marilyn Manson, because it builds dramatically (like Ravel’s Bolero, in a way), with an innocent musicbox melody that is overtaken by the foreboding bass/drums/electronica . . . much like the virus.