HiKayaker provided a good list above. I personally like the Pachmayr Decelerator and, not on the list, KICK-EEZ. KICK-EEZ sells a Magnum Recoil Pad that is offered in 1-7/8" and 2" thicknesses. They also offer stock pad spacers in 1/8", 1/4", and 1/2" thicknesses that you can use with any make of pad Pachmayr, LimbSaver, etc.
You can find "pre-fit" pads but my experience is that none of them fit well without sanding or grinding. If you don't have the right equipment I suggest installing whatever pad and/or spacer you like and then having a gunsmith grind it to fit the stock. Of course if you have the know how and equipment, more power to you.