Make a Rheostat
http://www.energyquest.ca.gov/projects/rheostat.html
Make a Telegraph
http://www.yesmag.bc.ca/projects/telegraph.html
The basic form and chemistry of a battery is easy to see from building one yourself from a lemon, a strip of zinc, and another strip of copper.
Lemon Powered battery experiments
http://members.aol.com/dswart/LED.html
How to Build a Power Pack
http://www.energizer.com/learning/science/experiment.asp?ExperID=875
Make a circuit
http://www.energizer.com/learning/science/experiment.asp?ExperID=876
Human Battery Experiment
Make Your Own Battery - Rough Science - Island Power Plant
http://www.pbs.org/weta/roughscience/discover/powerplant.html
Potato Battery
http://www.fofweb.com/Onfiles/SEOF/Science_Experiments/5-40.pdf
http://pbskids.org/zoom/activities/phenom/potatobattery.html
Beakman's Electric Motor
http://fly.hiwaay.net/~palmer/motor.html