(beta status indicated in the title)
DaylightMap shows the pattern of night and day on a Google map, for any area of the Earth, for any date and time. It also allows you to select up to ten locations on the map; in addition to seeing at a glance whether it’s daytime there, you can show their local time, sunrise and and sunset times, and length of day. These locations can be remembered for future visits, saved as a bookmark, or sent to other people as a web link. This site can thus function as a graphical world clock, and can be used to show relative times of any future or past event.