The only thing worse than a lukewarm drink is a watered down one. You can invest in cocktail ice molds (more on those shortly coincidentally), or just freeze these glasses in your freezer.
These cups aren’t slate, glass, or steel, they’re not even particularly pretty, but they work.
Update 12/1/17: Step up to the Rabbit versions for a much more premium look and feel.
Update 12/1/17: If you prefer ice over gel, the Corkcicle Whiskey Wedge delivers what you need in an elegant package, no ice ball molds required.