Warner Brothers Harry Potter "Screen Mate" Desktop ProgramPoA Film
In conjunction with the Time Turner Sweepstakes and the impending Prisoner of Azkaban DVD release, Warner Brothers has released a desktop program that lets you select from different screensavers, allows you to access pages of the official Potter website directly, drops the shrunken head down from the top of the screen to shout things at you, lets you play sound clips from the movie, and more. Click here to download.
I did a test download before posting, and I have to say I'm rather enjoying hearing Harry yelling 'Expecto Patronum!' over and over. :)