You need to add some different resolutions to the "screen" section in your XF86Config file. For example here is mine:
Code:
DefaultDepth 24
Subsection "Display"
Depth 8
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 16
Modes "1280x1024" "1024x768" "800x600" "640x480"
ViewPort 0 0
EndSubsection
Subsection "Display"
Depth 24
Modes "1280x1024" "1152x864" "1024x768"
ViewPort 0 0
EndSubsection
List your default resolution first in the line, under the subsection that lists your default depth. You can see in my example that my default is "1280x1024" at 24 bit colour depth.
You don't need to add the resolutions you don't think you will use. Now when you do the ctrl alt + - thing X will cycle through the resolutions you have specified here.