Not sure if this one has been done before, and it may be a bit more interactive. I think it would be fun to do a scavenger/treasure hunt themed one. This may work best on either a weekly basis or monthly. If you choose weekly, then have a different "item" for each day of the week. Same idea would apply for monthly, except just do one week a month.
Monday - I can be used to help keep your little one healthy, or maybe keep you updated on the latest text message. I love to fit into tight spaces, or stand out in the open. I add color and zaniness to your day. What am I?
Answer - A ZZ Be mine
(I know that probably wasn't he best riddle....
At the end of the week have everyone post their answers. Out of the correct answers, randomly select a winner.
You could also get wayyy more creative with it and use pictures of JJB's in the wild. This could be especially fun in December.