Science Buddies has many excellent science fair project ideas, some with very detailed instructions.  Here's a link to their project ideas section:

http://www.sciencebuddies.org/science-fair-projects/project_ideas.shtml

It sounds like he would be most interested in something in the Life Science or Earth & Environmental Science section.

Or he can use the Topic Selection Wizard at the top.  It will ask several questions about his interests, grade level and teacher requirements, then suggest projects best suited to him.

Science Buddies also has excellent sections on the scientific method and putting a science project together.