ColorVision's Spyder3 Pro. So you might be asking, why do you need to calibrate your screen? Well, as time goes on and you leave your monitors on for days on end or beat them up here and there, things change and they need to get calibrated. This Spyder device literally hangs over the front of your screen and a program runs showing off different colors and ranges, etc....The Spyder has a sensor that is reading the color as it's happening and the program adjusts it one way or the other to make sure that Red is showing up EXACTLY as Red and not Red with a little Orange. Once it calibrates each monitor it applies a Color Profile to each and from that point forward, the profile adjusts images being displayed so that the colors are spot on.
Make sense? This unit is the pro version which is needed for dual monitors and goes for around $150. For the average home user / casual photographer you can grab the Spyder 3 Express for around $90.