I realise that hardware calibration is the way to go but in the absence of sufficient funds, I found these pages helpful:
Monitor calibration and gamma Background to monitor calibration and gamma
Beware, though. If you are using a laptop LCD display, you may not be happy. Typically the gamma of laptop LCDs depends on the viewing angle and on mine I cannot get all three colour components corrected at the same time.
Here's a useful tool:
QuickGamma.