I've had great luck with "dancing through the decades", but that's with a high school crowd. We would begin in the 50's, then to 60's and so on... There's a surprisingly good choice of music to pick from that most kids enjoy dancing to. But a younger crowd is a bit more of a challenge. I'm actually in your boat. A middle school contracts to do a dance about once a month or every other month. It's tough thinking of new ideas to change things up. I'd be interested in hearing from others here as well.
Have you heard of a Sadie Hawkins dance? It a dance where the girls ask the boys to the dance and everyone dresses like hillbillies.
Have you thought of doing a field day event. Organize potato sack races, water balloon toss, scavenger hunt, wheel barrow race (this is where one kid is has hands on the ground and the other kid holds onto the legs), crab race (a race where the kids have to crawl opposite of normal crawl with the back facing the ground)
Do a google search for field day games for lots of ideas.
Parent and kid dance.
It's a small world. Kids dress up as someone from another country.
In past years, We've done Castaways, super heroes, zombie apoclypse, harry potter, end of the world, carnival, fire & ice, welcome to the jungle, the big 80's, New York New York, enchanted evening, Hollywood, prom around the world, and so many more..
Don't be afraid to think outside the box.. the students will appreciate it!