Anything you've done and you were even somewhat proud of it. It can de a drawing, sculpture, whatever. Explain it too, so the people know what you had in mind. I'll get it started...
I'm not much of an artist by any means, but I did this during my insomniatic night last night. I was trying to do a reflection off a lake or something that would portray the city of Denver from the mountains (If you live here you may be able to catch that better than most), just done with pencil and paper.