I've got this:
http://www.amazon.com/gp/product/B0002SQUHW?psc=1&redirect=true&ref_=oh_aui_search_detailpage
It was a lot cheaper when I got it, looks like the price has gone up. I have an acorn nut on the end to give a greater spreading range.
Spreading the pistons back is the hardest part of the job for me. I use this tool one the old pads to spread them back as far as I can, with a bleeder hose attached to one of the brake bleed screws to relieve pressure. You can also remove the brake master cylinder. But if the pads are really worn, and your brake master is full, you may need to remove some fluid, and allowing it to come out from the bleed screw is the easiest way for me.
Also when I bleed brakes after a track day, I use this to squeeze the pads back when I bleed, in case there are any air bubbles in the part of the line inside the caliper that is after the brake bleed screw. Don't know if it is necessary though
