Try these Internet sites:
http://www.super-science-fair-projects.com

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

http://express.howstuffworks.com/homework-scifair.htm

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

http://www.stemnet.nf.ca/~jbarron/jh.html

http://spacelink.nasa.gov/Instructional.Materials/Curriculum.Support/

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

http://www.scifair.com/