VR-Helmets

(This is the "hi-Res 800" from Cybermind)

I think this is what you might have expected as "Virtual Relity Device" (in contrast to the 3d-glasses).

These helmets have 2 small screens (most common used are  TFTs/LCDs) in front of the eyes: one for the left and one for the right. By showing (you might have expected that) 2 slightly different pictures on each monitor, the user will experience a 3D feeling.

This is a very expensive method. VR-Helmets mostly are expensive hardware thus making them only affordable for professional users and not us gamers - but prices are dropping, you can get the "hi-Res 900" for about $3000 for example.

(Dresden3D's 'D4D' 18.1" 3D-display)

These autostereoscopic devices also use the way to show the eyes two different pictures, but this is done in a completely different way. There is a very nice video that shows you how it works in a simple and understandable way: Click here.

Over at Stereo3D.com you can find a review on that device.

The vertically interlaced stereo-image goes through a prism-mask which is aligned according to the users position provided by an eye-tracker on top of the screen. In later versions the eye-tracker will also be used to allow some limited headtracking for looking around objects.

The price of these devices are...ehm... high. Very high.