All Science Fair Projects- this site boasts that it has "hundreds of science fair projects"; all grade levels
Discovery's Science Fair Central- everything you need to get you started
Earthquake Related Science Projects- from the US Geological Survey
IPL2 Science Fair Project Guide- step-by-step instructions
Prepare For a Science Fair- lesson plan for grades 6-8 from HotChalk
Science Fair Adventure- projects cover every category of science including mathematics and computer science
Science Fair Primer- getting started tips
Science Fair Project Ideas- from Education.com; covers grades K-12
The Science Project- ideas for 7th and 8th graders
Science Fair Project Ideas- choose from lists of easy, medium and challenging projects
Science Fair Projects- over 400 to choose from
Science Fair Resources- Science From Scientists
Science Fair Sanity- grades K-12 ideas for download
ScienceBob- this site has loads of "science stuff," and you'll find ideas, videos, research and experiments
Science Buddies- currently 1,073 ideas grouped by area of science
Steps of a Science Fair Project- yup, step-by-step