How to calibrate the monitor on an Ubuntu system?

You can use GNOME Color Manager to install color profiles, perform calibration and adjust color settings. For full functionality, you'll need ICC profiles that provide the required information for your devices.

If you don't use unity (or gnome), using gnome-color-manager does NOT work (see How do you set system display color profiles in Xubuntu and Lubuntu? for the glory details).

However, there is an excellent german howto all necessary things manually: http://wiki.ubuntuusers.de/Monitor_profilieren_mit_ArgyllCMS

I think that a ColorHug2 (http://www.hughski.com/colorhug2.html) is probably the best choice IMHO. I want something with Linux software out of the box and this looks like the right product.

I'm writting this so that other people googling will find the product.