I calibrate my monitor by going to sites that display test patterns and stuff, then just bring up my graphics driver, and tweak the settings under advanced mode. You can google for these sites, and they'll also tell you how to use the test patterns to calibrate your monitor. It's free.
Beware that for LCD screens, the gamma changes depending on your viewing angle, so calibrate the monitor to your most comfortable posture. Otherwise it'll be off when you're working on your pictures. The useful part of this "problem" though, is that you can "vary" the gamma on your monitor by just shifting your viewing angle. This will help to see if your dark or white areas have any details that are "hidden" and allow you to make adjustments to bring them out.