Flight Patterns is a data visualisation project by University of California, Santa Cruz alumn, Aaron Koblin. Using data from the U.S. Federal Aviation Administration he has created animations of flight traffic patterns and density with a beauty that belie their number-crunched origins. View the overview documentation video (quicktime) here.
Make sure to also check the 3D Blobular animation.
Also interesting: Still frames from Celestial Mechanics.