How about the opposite of Challenge 71 -- "Stillness." If we wanna get real tricky, do the same subject of Challenge 71 that you did, but still...no motion.
How about a 2-photo contest. Same subject, but opposite (in some way). One still, one in motion. One lighted, one as siloette. Objective is to achieve the best photo possible both ways. That way people who didn't participate on 71 can still play.