Some things I thought of that others thought of first and have done properly:
This lady does “paintings” in polarization of cellulose. (Yet another use for a laser etcher: draw the stuff in Adobe Illustrator and cut the cellulose with the etcher.)
I wrote a note on making a polarimeter out of blue sky and water, and also thought of a polarization clock to hang in a north/south-facing window. Here’s a combination of both ideas.