http://www.earthquakesound.com/tremor.htm

I know they isnt popular at all, but I picked up 2 12 inch TremorX and powered them with a JBL GTO 1200 watt amp. These things POUND! I want to say they hit harder than my punch hx2s but I'm using a different box. Unlike the Hx2s though they dont require a shitload of power to get loud.