X-Rite Optix XR2 Monitor Calibrator - PhotographyBLOG:

If you're not planning on printing your images, then monitor calibration isn't a huge deal - just edit the photos so they look good to you.

If you are planning on getting prints, or even printing on your home printer, you need to to invest at least a bit of time in calibration.

Both OSX and recent versions of windows include some basic tools for this - and you can probably get close enough for most people by using these. I also like to have a reference image - an image with a broad range of colours, that I have both electronic and printed - with a bit of eyeball work, you can pretty much verify the calibration of you monitor against your printed output.

I don't know about everyone else, but I feel these methods leave something to be desired - they feel inaccurate, there's too much eyeballing going on, and this is where tools like the X-Rite Optic XR2 come in. Connecting via UAB, this device senses the colours on your screen, and helps you get the monitor tuned right, so what you see on screen will match your printed output. Assuming, of course, that your printer is calibrated equally correctly.