Rubik's Cube Holder by Jerry O'Connell and PropDog - Trick
The holder will carry both a regular-sized cube and a speed cube. Unfortunately, due to its snug fit of a regular cube, it will not hold cube shells.
The holder has a belt loop, perfectly designed for those of us who wear belts (it can only be used if you are wearing a belt).
Holds regular 57mm 3" x 3" x 3" cubes.