I wanted a glowing head that would duck down behind a deck/bush and then rise up above it. By using a scavenged windshield wiper motor, I attached a 5 inch lever arm to give a 10 inch up and down travel. I used a glow-in-the-dark alien mask, styrofoam head(wig shop), and a flourscent black light.
I used a 12V Battery charger from Walmart ($20) to run the motor since you need ~3 Amps at 12V. I used a 10Watt power resistor ~2-3 Ohms to adjust the speed of the motor. I used PVC pipe (very light) to act as the up and down arms to translate the rotation into vertical motion. They is a transition piece with rubber bands to have it spring back into the right position. The upper vertical guide had a fair amount of friction and had to be oiled with WD40. I've run this 2 years in a row for a total of 10 hours without a problem, but I might go with a simpler mechanism described below.
I think going towards a string and pulley mechanism would run much more smoothly and reduce the friction. I think a drawer slider would work well to restrict the motion vertically. I haven't built this but it would probably run better.
Up and Down Alien Head (440k) Movie