Below is a collection of science websites. They are in no particular order but are all related to Grade 4 Science in some way or another.
A collection of online science games, two of which deal specifically with the subject of LIGHT http://www.iknowthat.com/com/L3?Area=L2_Science
Energy Do you want to learn about energy conservation? There are some interesting models you can build. You will study energy in grade 5. http://www.re-energy.ca
The Human Ear How it works. An animated website http://www.innerbody.com/anim/ear.html
General Science A variety of experiments on all types of science http://www.exploratorium.edu/snacks/snackintro.html
SOUND http://www.acoustics.salford.ac.uk/schools/
The Machine Detective [wheels, pulleys and levers] Experiment, make, test and learn about simple machines. You will like this website. http://oac.schools.sa.edu.au/eshop/machine/index.html
Some interesting experiments on 'seeing things' lots of fun http://www.exploratorium.org/exhibits/f_exhibits.html
Canada Science and Technology Museum Important science from a Canadian Perspective http://www.sciencetech.technomuses.ca/english/schoolzone/kidszone.cfm
The Canadian Museum of Civization Many excellent resources and activities http://www.civilization.ca/visit/indexe.aspx
MICROSCOPE Want to look through a microscope but don't own one....check out this virtual microscope....very interesting...explore the site as there is also a virtual electron microscope http://education.denniskunkel.com/catalog/
Brains Rule What do you know about your brain? http://www.brainsrule.com/
General Science To broaden your mind....and have some fun http://www.exploratorium.edu/