I just downloaded this last night and I've already noticed my eyes feeling better. For those of you, myself included, that use a computer for several hours a day, this is pretty awesome. It's free and downloads in a few seconds.
link to www.stereopsis.com
f.lux makes your computer screen look like the room you're in, all the time. When the sun sets, it makes your computer look like your indoor lights. In the morning, it makes things look like sunlight again.
Tell f.lux what kind of lighting you have, and where you live. Then forget about it. F.lux will do the rest, automatically.