This has nothing to do with kilts or Scottishness (hence the forum choice). Anyway, for those of you who are into power-metal, I just found an a capella power-metal group called Van Canto (there is a music video on their page).

Okay, they aren't truly a capella, as they have a drummer. But I don't think it is humanly possible to beat-box those metal bass drum kicks. Watch the video though, it really sounds like there are guitars!