Best Buy has an offer on for reward zone gamers club members for a free PS3 Dual Shock 3 controller. You simply need to trade in one select game. The list of eligible games can be found here.
The key here of course is to find a game to trade in that costs less than the price of the controller. This should be accomplished easily enough, especially if you picked up a few games during the boxing week sales.
You will need to bring the coupon found at the link below with you to receive the offer. You will also need to be a Best Buy Reward Zone member to be eligible as they will need to scan your membership card.
This offer expires January 10th, 2013.