I don't know if you'd call these dudes(and chick) metal beatboxers, but what comes out of their mouths is amazing.  Check out their full cover of Metallica "Battery" using on their voices and drummer.

I don't know whats up with all of these covers people are doing of metal(Du hast, Enter Sandman) but I'm digging it.  Also, this group, Van Canto seems pretty sweet.  Pretty cool gimmick and the chick is more than doable.