Try these Internet sites:

http://www.super-science-fair-projects.com

http://www.ipl.org/youth/projectguide/

http://faculty.washington.edu/chudler/fair.html

http://school.discovery.com/sciencefaircentral/

http://www.nasa.gov/audience/forstudents

http://physics1.usc.edu/~gould/ScienceFairs/

http://www.scifair.com/