Constructions - do you work with resources such as LegoTechnic with Year 8 or nearby levels? Or do you study simple machines like levers and gears? Give your students useful and fascinating activity with http://sodaplay.com/index.htm
To introduce Year 7 students to the elements go to http://www.uky.edu/Projects/Chemcomics/
Fun and learning related to
batteries at the Duracell site
http://www.duracell.com/
Glass - some science (e.g. uranium glass) and lots of art-craft museum-type information http://www.glass.co.nz/
Information about gemstones and gemmology http://www.geogem.com/
Pictures of mineral specimens from Michigan Tech at http://www.geo.mtu.edu/museum/
Natural Resources, Canada - comprehensive geological information http://sts.gsc.nrcan.gc.ca/
A Michigan Technology University site which deals comprehensively with volcanoes worldwide http://www.geo.mtu.edu/volcanoes/
Challenge your students to think scientifically by analysis of items presented as "junk science - faulty scientific data and analysis used to further a special agenda",. http://www.junkscience.com/ and also http://urbanlegends.about.com/culture/urbanlegends/
The Seaborg Centre has compiled several lists of Kid-Safe sites, many of which have science content. These would be a good place to start when searching for junior-level material. http://seaborg.nmu.edu/kids/
The exploratorium is a San Francisco museum of science, art and human perception (like Questacon, Powerhouse Museum or ScienceWorks). This part of the site contains cross-references between all the exhibits and the phenomena they illustrate. Could provide useful ideas for demonstrations or for student practical projects. Visit this part of the site at http://www.exploratorium.edu/xref/ The home page gives more information about the museum, including special exhibits. Go there if you visit USA.
If you can't find it in their home page index, look it up in their search engine. How Stuff Works is an extensive and most informative site. Ask your questions at http://www.howstuffworks.com/
An up-to-the-minute space page for kids is to be found at http://spaceplace.jpl.nasa.gov/spacepl.htm
Another simple level astronomy site worth a look is http://library.thinkquest.org/25763/mindex.htm
An impressive site about eagles, constructed by students at two Tennessee schools (with a lot of adult assistance). http://www.eaglewatch.com/
National Geographic online is as attractive as the well known journal. Includes lots of stuff for kids. See what is on offer at http://www.nationalgeographic.com/index.html
For the study of simple machines, in conjunction with other resources, go to this site which includes an "Inventors' Workshop". http://www.mos.org/sln/Leonardo/
Some fun projects and experiments for kids are described at http://freeweb.pdq.net/headstrong/
Entitled "Bizarre Stuff you can make in your kitchen", this site will provide plenty of fun/science activities for rainy afternoons. Find it at http://freeweb.pdq.net/headstrong/
If you are studying steam engines (e.g. in Scott Visual Physics package on Heat) look at the half-dozen excellent interactive animations at http://www.bbc.co.uk/history/programmes/dibnah/dibnah99/
The Beakman's World site seems to be a spin-off from a kids' TV show. A good place for primary students to browse, find answers to some questions, look at some interactive demos (requiring Shockwave), see some good space pictures...Let students investigate, then have a 'show-and-tell' session about what they found at http://beakman.com/
An attractive, illustrated online chemistry text directed at younger students http://www.chem4kids.com
Some interesting teaching material for upper primary level is presented by Dr. Mary Urquart; begin with Playground Physics at http://lyra.colorado.edu/sbo/mary/play/
Renewable energy for younger students presented at http://www.energy.ca.gov/education/renewableroad/index.html
Comparison of various energy sources in simple clear summary form at http://www.darvill.clara.net/altenerg/wind.htm
Airwatch is a national education program in which students monitor their local air quality. A hands-on involvement in data collection. Be informed, and join up at http://www.airwatch.mrwa.wa.gov.au/
Waterwatch Australia is another program for students interested in monitoring local catchments. Become involved at http://www.waterwatch.org.au/
Australian Forests Industry presents a site for primary students to learn about forest resources and forest management. A well-designed and attractive learning resource. http://www.nafi.com.au/timbertrek/
Watch this space for more great links for junior students