Marble Races with a cheap pool noodle (occupies the kids for hours.) Did this, but instead of cutting the pool noodle, the marble is small enough to fit inside the full noodle to roll down. Then can use the noodle for other things too!
The Ketchup Experiment! Kid friendly site with lots of neat experiments! It has one that makes a rocket out of a film canister, which would be good for an grade space unit, but it has to many kid friendly expiriments. Great site for any science teacher.
Fun Classroom Activities and Experiments to Interest Kids in Growing Plants
DIY Mini Mason Jar Aquariums Make waves and teach your kids about sea habitats with this cool and simple ocean bottle DIY. This is perfect for ocean themed parties or beach weddings. Such a fun craft for kids too!