The modeline that has worked 99% on my system is:

ModeLine "960×544/60" 40.3 960 992 1144 1176 544 555 561 572 +hsync

The +hsync at the end seems to be "optional", as I have been running it without and my subjective impression is that the image is much more stable.

Just to make this post complete, here are the most important changes I had to do to my /etc/X11/xorg.conf file manually to get 16:9 and 960×544 pixel on my screen with decent fonts in KDE and MythTV. Aditionally you can get the whole file klicking on the above link.

Modules

Section "Module"
Load "GLcore"
Load "i2c"
Load "bitmap"
Load "ddc"
Load "dri"
Load "extmod"
Load "freetype"
Load "glx"
Load "int10"
Load "type1"
Load "vbe"
EndSection

Monitor 16:9

Section "Monitor"
Identifier     "Monitor[0]"
VendorName     "--> LCD"
ModelName      "1280X1024@60HZ"
UseModes       "Modes[0]"
DisplaySize 325 182
HorizSync       28.0 - 82.0
VertRefresh     50.0 - 60.0
Option         "DPMS"
EndSection

Device (Nvidia without autodetection of DPI)

Section "Device"
Identifier     "Device[0]"
Driver         "nvidia"
VendorName     "NVidia"
BoardName      "GeForce2 MX 100/200"
# Making Fonts work for MythTV
Option "UseEdidDpi" "FALSE"
Option "DPI" "100 x 100"
EndSection

Update 28. May 2008

I used to have my Sanyo connected to a VGA splitter, that would enable me to use my CRT monitor on one cable and the projector on the other. Via xrand I would then change the display size to reflect the one I was using. This has now changed, and I upgraded my old Monitor to a DVI capable Belinea 22 inch and my video card to a nvidia 8600 GT. After a few days of fiddling arround I got both screens working in paralel. That way I have two desktops, one 16×10 and a 16×9 for the projector at two verry differen resolutions. Check out the xorg.conf file to see what I did. The magic is again in the custom modeline.

I run my HTPC using SuSE linux. To get my video card to access the my Sanyo Z1 projector directly I needed a modeline that would make it switch to "PASS TRU" mode enabling the real 960×544 pixel ratio (16:9) without scaling. Under Linux this means that you have to edit the xorg.conf file usually in /etc/X11/