Mine's a screen-capture from Beethoven's "Pastorale," from the original "Fantasia"...I caught The Moon/Artemis-as-huntress, with the little stag by her side, right before she releases an arrow to become a shooting star.
Due to the age of "Fantasia," the screen-cap looks rather a lot like it was done in either pastels or watercolors. It's been there since I got this computer several months ago...and I don't have the heart to change her.
(And if anyone wants a copy, e-mail me...I don't mind sharing! I also have several other screencaps from the original Fantasia and Fantasia 2000 that serve as my screensaver.)
Now at work, I have a nifty photo-shopped pic that someone did compositing Cinderella's castle and a fireworks display...prior to that (and will probably return to this after my trip), I had Gerard Butler as the Phantom and Emmy Rossum as Christine from the new "Phantom of the Opera" movie.