A 3D rotating cube I whipped up for a 10K JavaScript contest in August of 2010, which I never submitted. I always wanted to code something in 3D so once I managed to get it working, the excitement of competing wore off and I didn't bother submitting it. It's only 6.9K and 1.9K minified, so I'm sure I could bring it down to 1K for a 1K competition, if I cared enough to compete. :)
I should mention that Mo Kakwan helped me out with the math.