I know Heavy Metal is American, who the hell couldn't tell. If it was Japanese it would be Heavy Techno-Pop or something. But it's still anime for it's style, the same thing for Aeon Flux and The Boondocks.
I second that. I always liked Piano Black, the one that goes "Where's you messiah, w00t" (Blue I think it's called), and 24 HOURS OPEN.
EDIT: I just uploaded 24 HOURS OPEN to youtube because no one had it on there.
http://www.youtube.com/watch?v=JHDw1dteigA