This is very important, because it's hard to see details if your monitor is too dark. I've found some simple tests to help, here's the links.
Gradient testing, from black to white: http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm (http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm)
Different levels of black and white: http://bryce-alive.net/calibrate/ (http://bryce-alive.net/calibrate/)
Color gradient test: http://www.stanstudio.com/calib.html (http://www.stanstudio.com/calib.html)
LCD-specific tests (color, grayscale, gamma, contrast, grayscale, viewing angle): http://www.lagom.nl/lcd-test/#gradient (http://www.lagom.nl/lcd-test/#gradient)
Hope these help ;)
adobe also has a gamma calibration
http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=321608 (http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=321608)