DiscoverySchool.com:Science Fair Central
http://school.discovery.com/sciencefaircentral
"A comprehensive guide to creating your science fair project!"

Eastern Newfoundland Science Fairs Council
intermediate (gr. 7-9)    www.stemnet.nf.ca/sciencefairs/intermed.html 
senior (gr. 10-12)  www.stement.nf.ca/sciencefairs/seniors.html

Internet Public Library 
www.ipl.org/div/kidspace/projectguide
"The IPL will guide you to a variety of web site resources, leading you through the necessary steps to successfully complete a science experiment."

Science Fair Central  
www.homeworkspot.com/sciencefair
General science fair sites, project ideas listed by subject, and resources by grade level.

The Science Club: Kids' Science Projects
http://scenceclub.org/kidproj1.html
Arranged by level of difficulty (simple, medium and advanced).

Science Fair Projects
http://www.all-science-fair-projects.com
This site has over 500 fully searchable and categorized science fair projects, with full instructions and explanations. You can search for ideas for your projects by simply entering a keyword on whatever interests you.

Science Fair Projects Index
http://ascpl.lib.oh.us/scifair/sftp.htm
Search by subject, experiment type, and/or grade level.

Ultimate Science Fair Resources
www.scifair.org 
"Whether you are a student trying to find an idea for a project, a parent or teacher looking for information on building displays, or a science enthusiast who enjoys the delight of experimentation you'll find what you're looking for here."