I came across the French website Focus Numérique which offers freely downloadable icc profiles for some monitors and laptops. You can use them with xcalib on your Linux system. It assumes that you keep your monitor settings as from the manufacturer.
It is not as good as owning a colorimeter – since calibration varies over time and from sample to sample. But still, it is much better that the poor man’s calibration – that is, if your monitor is in the available models.