The movie site just put up a screensaver commemorating the 15th anniversary. Just scroll down to where it says "Windows" or "Mac" and click on one to download it. The installation instructions are in English, so don't worry about needing to know Japanese.
As you can see from the screenshot on the left, it's pictures of Pokemon from all the movies, with a big Keldeo clock in the middle telling you the current time. Not the fanciest thing, but I think it's pretty cool.