How about something by Yngwie Malmsteen? He's a fairly well-known heavy metal guitarist from the early 90s, known for a neo-classical style. His guitar work has a delicacy that contrasts with the heavy, crunchier style of his backup - it could be a good combination for CLAMP. He's also fond of apocalyptic themes. You could try "Cry No More," Forever is Long Time" or "Final Curtain," from FIRE AND ICE, or "Seventh Sign," the title track from the eponymous album of the same name.
It really depends on what knid of video you want to do; sometimes the song births the concept, sometimes the concept forces your song choice.
Nevin