Well organized list of ideas by subject (electricity, math, life sciences, etc.)
One explanation of the laser pointer sound experiment
Explore this weblog deeply for all sorts of year-round ideas, science fair included.
Power a super-bright LED from a low-voltage battery with a few bits of wire and a toroid core
Some ideas here for 3rd graders who have studied sound
A fun project from Spark Bang Buzz, good for 4th grade. Explore the site for more inspiration
Great resource for parts and kits