Short of a sheet metal break, the best thing I have used is a Dremel reenforced cut off disc. It must be chucked in a drill press, and I use an "L" shaped piece of Aluminum as a backstop. Just set the table so the pc board is vertically at the right height, and run the board through standing up. It creates a clean edge and little waste. Just don't breathe the dust, it is very irritating!