Exploratorium
Exploratorium: Science Snacks: Snacks From a Z
Here is a monumental list of ideas for science fair projects and experiments, organized alphabetically. Every one of them is a link to a full page, with pictures, of information about the idea. This site is a goldmine.
Other
Science Fairs Homepage: Senior Projects
This resource from the Eastern Newfoundland Science Fairs Council provides really substantial projects for senior High School students. These are online topics, six areas, with about 10-20 topics per area.
Discovery Education
Discovery Education: Science Fair Central: Validate Topic
A small collection of questions students should ask themselves as they think about the topics they want to explore in their science fair projects.
Discovery Education
Discovery Education: Science Fair Central Choose a Project Idea
This helpful page from Discovery Education provides science fair ideas in Life Science, Earth Science, and Biology. Testable questions to get you started are listed beneath each domain.
Discovery Education
Discovery Education: Science Fair Central: Choose a Project Type
For your science fair project, you can try inventing something or you can investigate a scientific issue. Find out whether doing an invention or an investigation is right for you.
Other
Cdli: Science Fairs Homepage
At this site from the Center for Distance Learning and Innovation there's a monstrous listing of possible science fair projects. You can choose from primary (grades 1-4), elementary (grades 4-6), intermediate (grades 7-9), or senior...