SunsetScreen
SunsetScreen is a free Windows app (for personal use) which helps take the glare off your your screen in the evening. Scientific research has shown that melatonin - the chemical the brain makes late in the day - is reduced when exposed to blue light. By tempering this blue light, it becomes easier to wind down properly at night, and thus have a more restful sleep.
Whether you're a morning lark or night owl, SunsetScreen allows you to set the time of the sunset and sunrise, so you can have full control over your sleep cycle.