Emilio Gomariz is an artist who's used the window animations in OS X to create some pretty amazing abstract art. You can look at the YouTube videos to see just what he's done, but my favorite is the one above, called Twist Choreography. To create it, Gomariz opened up a series of long, thin windows from the dock, spinning them out into an orderly stack. There are others, too, where he uses Expose or other OS X tricks (you can make the window animations go slow like this by holding Shift, in case you hadn't heard that yet) to create beautiful patterns as the windows grow and shrink.

It's very impressive work, and it shows not only just how creative Gomariz is in terms of putting these things together, but how beautiful the most basic features in the core interface of OS X is as well. There's a lot of creativity here, both from the artist himself, and from the UI designers who helped put OS X together.