Unfortunately, since this is promo work, I think you're probably pretty constrained by the styles of the genre, which means a lot of leather, a lot of candid or faux-candid studio shots, and the obligatory group portrait of all of them looking disreputable and menacing. It's the commercial-photography problem---promos are the wrong place to be artistically adventurous...
But it might be fun just to mix in some high-contrast, gritty b&w street-esque material of the band members, for instance. The kind of stuff you'd see routinely for an East Coast hardcore band, and not so weird as to threaten the viewer's image of them as a metal band, but Something A Little Different nonetheless.
I would tend to avoid unexpected props...although the image just jumped into my head unbidden of the band gathered around a morgue table dissecting a giant Hello Kitty, and you may do with that thought what you like, I guess!