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.

Here's a fun project that combines baseball and math. Major League baseball is played in ballparks that have their own individual quirks when it comes to the exact layout of the field. Fenway Park in Boston has the famous "Green Monster"...