I've found that free stuff will really entice guests to extend their stay in addition to a room rate reduction. We offer a Sunday Stay-Over Special that includes tickets to a local music show, free pizza dinner, and a 10% reduction in the room rate. That way guests have something to do, they get a free meal, and a bargain on the room.
We talked to the owner of the music venue and he gives us a steep discount on the redemption of the free tickets. The local pizza place has a brown bag special, which is a large pizza for only $6.