As of a short time ago, SpaceX made history as the first entity *ever* to successfully re-land the initial stage of an orbital rocket.
Up until this point, the dominating factor in the cost of Rocket Launches has been that you have to build a new Rocket for every launch (about \$50 Million for a Falcon 9 launch, I've seen estimates of \$10 - \$20 Million purely to manufacture the rocket), whereas a typical launch burns just $200,000 of fuel.
If, in theory, Falcon 9 can continually re-use its initial rocket stage without having to build a new one each time, how much might this reduce the cost of a Rocket Launch by?