Monitor Calibration

Sorry to take it to this forum, but my D800 is so extreme that it pushes me to review my whole workflow environment.

I have found that whichever file setting (adobeRGB 98, sRGB, prophoto RGB, etc...) I use to export my developed D800 raw file with LR4.1, the saved jpeg always look different from my picture on LR4.1 screen.

I believe this is a screen calibration issue. I noticed the issue before with my D200 files but it was much milder.

So I would like to calibrate my monitors properly.

Any opinion about what may cause it and also about good ways to calibrate the monitors? I am using HP 27'inches LED monitors.

Thanks in advance for the answers.