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!
Spiegel in de bouwhoek - A Reggio Emilia-Inspired Classroom using a mirror in the block play area so children can see themselves while building. This also allows children to easily see their constructions from all angles.
Science/Small Manip - Creative "racetrack" for cars. Creates a secure platform for children to race cars down the ramps. Children could extend this to use different items (balls, blocks, marbles) to see how quickly different objects roll down the ramps.