I'm at work and just checked my white 20" iMac. Manufacturer is 0610 and model number is 9C59. It can't be AU Optronics, so maybe LG.Philips since the white 20" is known to have either LG.Philips S-IPS (same panel as the 20" ACD) or Samsung S-PVA panel. Either the manufacturer code is meaningless or some 2009 20" use something other than AUO.
For those of you wishing to find out the panel info, do the following:
1) Go to System preferences
2) Choose Display
3) Choose Color
4) Open Profile
5) Scroll down to number 13
The manufacturer code is meaningless. My code is also 0610.
My model number is 9C92.
I think Jay your info just figured this thing out. I am going to run a calibration test now and do use terminal to figure out my model number.