Most LCD monitors have one recommended resolution, so you should figure out what that is for your monitor and use it. You also need to make sure your video card is capable of supporting that resolution.
In your xorg.conf, in the Monitors section, comment out any HorizSync and VertRefresh lines.
In the Screens section, add the recommended resolution. For example, if your recommended resolution is 1440x900, you Screen section might look like this:
Code:
Section "Screen"
Identifier "Screen 0"
Device "videocard0"
Monitor "lcd0"
DefaultDepth 24
Subsection "Display"
Depth 24
Modes "1440x900" "800x600" "640x480"
ViewPort 0 0
EndSubsection
EndSection