There is a viable alternative to expensive shutter glasses. If the left and right images are polarized oppositely, the glasses needed are simply pieces of glass or plastic. I would favor circular polarization (left handed and right handed), so it can be viewed with your head in any position.

Think of light as pennies flying through the air. Some are vertical, and some horizontal. Our filters have slots in them for the pennies, either vertical slots or horizontal slots. When the pennies hit, only half get through. The others hit the slots crosswise and bounce off.

Many better quality sunglasses are linearly polarized. Most naturally occurring light is randomly linearly polarized. A vertically polarized filter eliminates about half of the light. So will a horizontally polarized filter, but it's the light the other lens lets through.

To see this in action, get two pair of polarized sunglasses. Wear one pair and put the other pair in front so you're looking through both lenses. Now rotate the second pair from normal (horizontal) to vertical. The view goes from slightly darkened to black.

So using vertical and horizontal polarization for 3D will work, but only when your head is perfectly vertical.

Fortunately, there's an easy way around this. Circular polarization. Instead of coming at us vertical or horizontal, this light is spinning to the left, or to the right.

If we take a lens with left hand polarization and another of right hand polarization, it doesn't matter how we turn them. No lights gets through.

If this is confusing, here's an in depth article with tons of math. You don't really need the math. Just look at the pictures.

http://en.wikipedia.org/wiki/Circular_polarization

Here's a 3D system using circular polarization.

http://en.wikipedia.org/wiki/RealD_Cinema

There are several methods that I know of for implementing circular polarized 3D. There are probably more that I'm not aware of. One is to use two monitors with CP filters, and combine their images using mirrors. Another is to use two CP projectors and a silver screen (normal screens use reflective material that disrupt polarization). A third method would be a single projector with a spinning polarization filter. Many projectors already use spinning color wheels. Or we could use a really large wheel for our big screen. <--- JOKE - no flames please.

The iZ3D H220z1 is a 3D CP monitor. It uses 2 stacked monitor screens, the front sans backing. The review I read (as a gaming monitor) was generally quite favorable. I went to IZ3D's site. They've discontinued it, and didn't give any reasons. There are still some in stores, as low as $279.

Even though discontinued, this proves the concept of a display for circular polarized glasses. They're cheap. IZ3D sells theirs for $12-$15.

-Mike