Want the effect of the skylight or window where there really isn't one? This could either be really tacky or a unique feature in rooms that can't receive any natural light, like the basement...
Skyceilings use a ceiling grid system with high resolution outdoor photography, backlit by a 6500K fluorescents or 6000K LED lighting system in a lightbox structure, creating not only the illusion of an overhead scene, but also providing illumination with the same light spectrum as real daylight. You can peruse the Sky Factory's catalog of different scenes here
We'd like to see a future version from the The Sky Factory using OLED display or similar technology, which would allow for more immersive and believable sky with moving clouds and swaying trees. Because as beautiful as one view may be, if it never changed, it would get a bit boring.