I scrap cars, they allow the cars to have tires on them, and extras I have around I throw in the truck or under a pile of "stuffing scrap" inside the car.

Also, I have heard it is legal to take tires to the landfill as long as you take a box knife and cut the sidewall off of the tread portion. My uncle and I did this with tractor tires using a sawzall, and I know of an auto repair shop / auto salvage yard that does this as well... so apparently it is legal here in Indiana.