how much do you want to lower? an adjustable panhard bar may be required. to do it right, you would get one anyway, but if you lower the car with the least amount of drop, you might be able to get away without one. also, depending on the amount of drop you might need different shocks/struts. for the best ride, adjustable shocks/struts are the ticket. you will also need to check the pinion angle. if the pinion angle is out of adjustment, then you will need an adjustable upper control arm.
all of these parts depend on the amount of drop. the lower you go, the more parts that are needed to complete the job properly.