The necessary general steps for completing a good science project are summarized at the Cyberfair. (Yes, I know it targets younger students, but it is still one of the better summaries of what you need to do. Add a requirement for a log book of your investigation and this will still serve you well.) Check your local guidelines for additional required features. The Internet Public Library's science fair project guide is a good site for an overview of science fair project concepts; the introductory science project site walks through the project process with links to a science example.

So you know what you need to do, but can't think of an idea? All of the sites above offer ideas, but I think the Science Club is a good place to start looking for quick-and-easy ideas. (However, you do risk ending up with a duplicate project; everyone else is free to use the same easy-to-find ideas.) Additional sites for ideas are the Science Fairs Home Page,  Ultimate Science Fair Resource, Rusk's Science Fair Resources, Science Fair Idea Exchange, Science Project Guidelines and the Science Fair Primer.

This is only a small sampling of the resources out there. Any general search engine will find many more ideas and resources using the key word "science project" or "science fair" Google is a good place to start because site suggestions ordered by PageRank type evaluations. This process tends to give site suggestions that are easier to figure out. However, this also means that you have a higher chance of getting an idea that someone else in your area already found. Don't skip using some of the other general search engines.