How to retrieve data for ModeLine?

In the Handbook in "Configuring X11" one can read how to hint Xorg to recognize correct monitor resolution.
There is a sample there (under section "Monitor"):
ModeLine "1680x1050" 146.2 1680 1784 1960 2240 1050 1053 1059 1089
According to the Handbook the data comes from /var/log/xorg.0.log
however there is nothing like this in my xorg.0.log.
I inserted exactly this line above in my xorg.conf and it works "as is" but it works only in Gnome, KDE crashes and restarts Xorg back to login screen.
Does somebody know how to retrieve the ModeLine data from a particular monitor?
Any help appreciated...
try man gtf
gtf 1024 768 75 - bring back modeline for resolution 1024x768@75mhz + the other things you request ;)
I would expect KDE not to work for a different reason.

By the way, it's a rare case that you need a mode line at all. If it shows up in your Xorg.0.log you certainly do not need it.

However, if you want a proper mode line you better take your search engine of choice, your monitor specs and search for a modeline generator.
Thanks a lot guys! I tried all 3 ways and I got different values for pixel clock and timings but none help KDE4 to work. It works however @1280x1024 if remove any xorg.conf. Indeed it could be KDE's problem not Xorg.
If somebody has the same problem, my monitor is SyncMaster2253BW, 1680x1050x60Hz(default), max pixel clock 146MHz, HorizSync=30-81, VertRefresh=56-75, video: GeForce8200(on board), MB: M3N78-VM, AthlonX2-2300MHz (4450e), DDR2-800x4GB, FreeBSD-8.0-current-amd64.
You say that you suspect that the problem is with KDE and not Xorg. This would be easy to test by running a different window manager just once (e.g., remove your .xsession before starting X).
I was waiting for 7.1-RELEASE and I have installed it now. Everything is working perfectly so far: Gnome2.24 (updated from 2.22), KDE3.5.10, KDE4.1.4 (available now in packages in ports). I keep using values from the Handbook for my ModeLine.
Anyway it was very useful to learn about ModeLine matter.
Many thanks again!