If you guys don't have this software, well, I guess now is the time to remedy that?
f.lux: software to make your life better
You set your time zone, and at night it will decrease the color temperature of your monitor from whatever it is, all the way down to 3400K (halogen), which makes it have a nice sepia tint. Especially if you do a lot of reading with black text on white background, this will save your eyes.
I've used it for a few months, and I no longer have headaches and my eyes are no longer feeling strained when I am reading at night.
It only does it at night, and If you are doing color sensitive work you can temporarily disable it also.
If you want you can decrease your monitor color temperature at day time too, but manually.
Update: There is also a new beta version which the temperature can go all the way down to 2700K, which is incadescent I think,