I went to the local fabric store and bought some really thin (muslin?) material that I cut and put through knitting hoops. I placed them in my windows and shown two projectors (one at each hoop) from the rear that projected eyeballs from the DVD "Terror Eyes":
This year, we are buildling on the monster house, but we will likely use the eyes again. The picture doesn't really do it justice, because the eyes were split from a common source, so moved together. I also had a speaker aimed out of one of the windows where a booming deep voice proclaimed evil to all trick-or-treaters. There was one kid who wouldn't come up to the house because he was scared!
I used a cheap semi transparent curtain and it works very well. I uploaded my haunted house this year on youtube. Its all controlled by my house computer using Insteon hardware, Homeseer software and custom .NET scripts. In previous years many trick or treaters would not come to my door because it was to scary. This year i will trick them by having the lights dim and the effects go off when they reach my front door. Ah ah ahhhhh.. The sound effects didn't record very well on the video but its really creepy in person. I guess i have to much time on my hands. :-)