Shutter glasses are next to anaglyph glasses the two most important technolgy for the 3D porn surfer (followed by side by side or crossview technology).
Whenever you see "Nvidia" posted on one of those porn website's (or in my review HERE), you'll be dealing with a website offering the movies in shutter glasses format (most of the time, websites offering Nvidia porn will also be offering anaglyph format).
Shutter glasses use liquid crystals to very slowly alternate between your left and right eye (in other words, one eye will be blinded while the other one can see, in an alternating fashion).
Nvidia (shutter) porn shows real colors, full 3D view, in HD quality. It's not even that expensive (last time i checked, about $150 for a full Nvidia kit, delivery and some 3D porn to go with that).
An other positive point is that you can keep your monitor, as long as the refresh rate (the amount of Hertz) is high enough.
Altough it's not expensive, it still costs a lot more than anaglyph porn. Also, it's a little more exhausting for your eye's than some other techniques.