If you own a rifle or shotgun, and love shooting it, but want less recoil. then the Remington Supercell recoil pad is the one for you. It's not a slip-on pad, it's actually a replacement pad for lesser-quality factory recoil pads. I put one on my Express 870 magnum and it tamed the beast quite well, reducing recoil by about half. It's a great deal too, only $20 from the Remington site.
Don't own a Remington? No worries, the next option is a great one for all rifle and shotgun owners, but it's not a recoil pad. The picture below is of an insert in the butt of a rifle or shotgun, called a mercury recoil reducer.
They are more expensive, but still reduce recoil greatly, and it's hidden so nobody would ever know. The only downside is what I sometimes hear on the gun range, what sounds like a wet cough. This is from the acoustics of a mercury recoil-reduced gun, and I don't particularly enjoy the sound. I like a nice clean bang.