The Holding Pattern Screensaver (available as a free download for Mac or PC), created by Los Angeles artist Cathy Davies, makes art that moves out of your computer's idle time:

The Holding Pattern Screensaver turns your idle computer screen into an airplane window, complete with a moving aerial view. Every time the screensaver launches, it plays a unique sequence of realistic, subtle animations.

I've only tried and tested the Holding Pattern Screensaver (you can upgrade to a version that runs without the occasional "nag screen" for a small fee, by the way) but Davies offers several other free downloads on her site, which is a screensaver development project "founded on the belief that screensavers are a hybrid form of cinema and installation (pun intended)--a unique and underexploited medium."  

Remember to adjust your screensaver preferences if you want to take "a relaxing meditative trip around the world," as Davies phrases it. If your timing is off and (like me) you're rarely idle, you may never get your window seat.