I use this project when I do my unit on Sports. This unit's grammar section is informal commands (both affirmative and negative). This project involves "inventing" a new product and then creating a poster or "ad" for it. The goal is to include three affirmative and three negative commands. This project is really neat because it forces students to get creative and use the commands in a more real life situation. They will have to think about how to inlcude the commands in a way that makes sense. This project can be adapted in terms of the rubric/grading scale. You can always have them include more or less commands or give them a specific theme in which their "inventions" must fit.
I have seen some very unique projects come out of this! Enjoy!