Check out this great Pi powered Halloween scarecrow form Chris Osborn:
I thought it would be fun to setup a prop on my porch for Halloween that did more than just sit there. Of course I came up with the idea very late and so this whole thing was cobbled together in just an hour or two. Looking around my house at a ton of the gadgets I had the idea of putting a Jack-o-lantern on the porch that I could control the light in. Searching the internet for scary Halloween sounds caused things to quickly evolve into adding motion sensors, controlling a couple of lights, adding sound, and putting the pumpkin in the lap of a headless scarecrow.