The Knoxx Spec-Ops stock is outstanding in my opinion. It gives you a collapsible stock that will go from being slightly shorter than a youth stock to full length. Recoil is dampened by a recoil spring in the stock. The receiver of the gun actually slide back into the stock against the recoil spring. The stock comes with a buttpad and you can buy other accessories for it like a shell holder, raise cheek rest, etc.
What the stock does is to decrease the the recoil impulse sharpness and speed by spreading it out over a longer period of time.
I don't use the buttpad on mine and like to run the gun with the stock fully collapsed.
The only real complaint I have seen is that it does change the recoil angle slightly and some folks get their cheeks bumped during recoil. That stops with familiarity of use.
Last I checked, they run about $120. Also, this stock may not work with enertia based semi-auto shotguns.