Here's another idea for one:
Creative 'make-something' challenge. Not like a trick or flourish, but a card or magic related thing. Some examples could be... a giant house of cards, a pretty (magic related) picture, a decorative collage of cards or maybe a silly hat made of cards. Then put up some pictures, or even take a video showing of your creation!
It'd be cool to see what some people create, I think.