My friend over at lokuhetty.blogspot.com recently bought a new LCD monitor and we have been banging our heads together to find a decent monitor calibration tool. Most of the freeware utilities out there are for windows and every tool that we tried was too complicated unless you are an expert photographer/graphic designer.
Monica (http://www.pcbypaul.com/software/monica.html) is a simple utility that works on Linux. Compared to other programs that we tried, monica is very easy for average people like us to use. All you need to do is squint at the image shown and adjust the sliders until the image shows a smooth gray gradient without colour cues.
Installation is easy as well. On my Fedora machine, this is what I did to install monica:
tar -jxvf monica-3.6.tar.bz2
sudo yum install fltk-devel
To run, just type monica
Happy calibrating !