Researchers at the University of Paris' Materials and Quantum Phenomena Physics Laboratory  demonstrate a "skateboard" that actually hovers, thanks to the forces of quantum levitation. In a nutshell, the interaction between the magnetic field (the rail) and a superconductive object (the board) creates a phenomenon called quantum locking, where the board is "trapped" in mid air relative to the rail. They call their Back to the Future-style hoverboard the "MagSurf."

Quantum trapping is explained and demonstrated, using small UFO-shaped superconductors, in this video from the superconductivity group at Tel Aviv University. As you can see in the video, the dramatic smoke is actually the liquid nitrogen used to cool the disks to -301ºF, at which point they become superconductive. At about 3:00, they add a little magnetic speed bump for the traveling disk, and at about 4:15, they demonstrate how the disk can travel above or below the track. 

Here is a live demonstration of the same setup:

While the necessity of tracks and a continuous supply of liquid nitrogen limit the possibilities of the hoverboard for the time being, it seems it might be only a matter of time before this Back to the Future II scenario becomes a reality.