Hack A Day is a fount of awesome mods and game themed creations, featured here frequently, and this portal gun which "levitates" a companion cube is one of the best conversation pieces they've come up with yet.
The construction is simple, really. They took a commercially available portal gun replica and fitted it with the coil and magnet from one of those levitating globes you can find in any dentist's office. The Companion Cube is made of foam. Simple and elegant.
Hack a Day's Portal Gun Actually Levitates a Companion Cube [Hack a Day via YouTube]