Since I had setup a lot of spider webs in my front door, essentially making it look as if you are walking into a cobweb, I figured a large spider was in order.
Step 1: Making the spider
I fired up Google Sketchup, as it can work as great and easy line drawing program with a mirror function. It also allowed me to layout my frosted glass panel to scale and visualize how large I wanted the spider to be on the glass.
I drew a cool looking spider, and a few minutes later I had a to-scale print out to use as a guide to cut my cardboard.
The template I made is online here: http://sketchup.google.com/3dwarehouse/details?mid=f25f707c99ef38358b62e185294e8b2e
Step 2: Setting up the dropping spider.
On Halloween night I wedged a PVC pipe against both walls.
I made a crude pulley by applying tape to the PVC pipe.
I used garden twine to suspend the spider.
I used a spot-light to back light it, it makes a VERY strong silhouette from the outside, vs standard house lighting.
The spot light was used to anchor the spider up just enough to catch your eye.
When the door rings I walk up and pull the string before approaching the door. The spider drops quickly to the bottom of the window, just about eye height on a kid.
It made for quite a few screams and a few people jumping back. Some had to have me show their kids it wasn't real. (Sorry)
It cost virtually nothing, took no time at all to do and was very effective.
Next year I think I will make the spotlight flicker before I drop the spider, just to make sure people's eyes are on the door when it drops.