Tovolo ice sphere molds. Make giant spheres of ice the size of billiard balls. Great for keeping hard alcohol cool, as spheres have the lowest surface area to volume ratio. Learn more at http://www.tiotil.com/content/tovolo-ice-sphere-molds
Zoku Ice Sphere Molds, Set of I had some other sphere ice molds, but they weren't silicone, and so if you didn't fill it up *perfectly* (and you had to guess what that meant) it would expand too much and crack the mold. These look much better.