Those classic red and blue 3D glasses are still useful! But where the heck can you find a pair in a pinch? Don't worry, with an old CD case and a couple o' sharpies, it's ridiculously easy to make your own.
It's dead simple: you need a clear CD case (or any sheet of clear plastic, really) and red and blue permanent markers. All you need to do is fill in a square of red and a square of blue on the CD case, and you're off and living in the 3rd dimension. Watch how it's done:
If you want to step up the style factor, you can buy a pair of clear goggles and mark em up too. [Labnol.org]