power: Restart, sleep, or shutdown.

command-power: Generate non-maskable interrupt, which will drop you into the built-in debugger or Macsbug (if installed). Type 'g' and press return to continue. (from macfaq)

command-control-power: Restart. (from Sad Macs, Bombs, and Other Disasters, 4th Ed, pg. 929)

command-control-shift-power: Restart. (from Sad Macs, Bombs, and Other Disasters, 4th Ed, pg. 929)