Lots of boxes/crates
Extension cord
Light bulb
Light socket
Monster costume
Sound device (optional)

As the guests enter this room they see what appears to be lots of boxes and crates. There is a single light swinging back and forth from the ceiling. When the group passes by one or more of the boxes, an actor or prop pops out of the box. To make the light swing, simply have the person who pops out of the box swing it before they get in to their box, or add a motor and fishing line.

Note: this room could also take on the appearance of a nursery, and have a very large jack-in-the-box.