Videogen is a small but nice utility to create modelines you can insert into your xorg.conf and fb.modes files.

Modeline is created by telling the program the resolution you want and your video hardware parameters (maximum video adapter bandwidth, maximum HCF and VCF of the monitor etc).

Note that for most modern installations, Xorg will handle its own modesetting automatically, and you don't need videogen to generate any Modelines.

The tool 'some_modes' may help you to create some common modes fast.