General Science

Some links cover more than one science area. I have put these in this classification.

Science Playwiths
http://members.ozemail.com.au/~macinnis/scifun/index.htm
Good to be able to put an Aussie site up there at the top. A real pot pourri of some old some new some just plain good fun. If you take the time to subscribe to the oz-Teachers list you will come across Peter Macinnis, a most interesting bloke. Not only a great collection but the science behind everything is clearly spelt out. A MUST VISIT............ 
BrainPOP
  http://www.brainpop.com/
This site has a number of interesting animations, (and also quite a few ads). Though they take some time to dowload they are pointing to the way of the future and very useful now. Check them out.
Whelmers
 http://www.mcrel.org/whelmers/
A selection of some excellent activities from what looks like a very interesting CD. The downloadable activities would make great ideas POE's plus they also have excellent explanations of the science behind the experience.
Reeko's Mad Scientist Lab
http://www.spartechsoftware.com/reeko/
Another collection of activities that many might have seen before. A lot racier than dear Peter Mac but interesting nonetheless. When you loasd the page scroll right to the bottom for the activities.  
NSTW
 http://www.nsf.gov/od/lpa/nstw/teach/start.htm
The teaching activities page of the American National Science and Technology Week has links to the last four years activities. 
OnLine Experiments
http://littleshop.physics.colostate.edu
/Experiments.html
Starting to look a little dated but uses the computer in an interesting way. 
K-12 Science Lesson Plans
 http://www.sciencegems.com/
An interesting collection from one of the Internet greats, Frank Potter. Not extensive but some interesting ideas on how to use the Web for science based activities. 
Cool Science For Curious Kids
 http://www.hhmi.org/coolscience/
Despite the big title, has only 5 activities looking at Butterflies, Plants, Microscopic Life,  Breathing and Animal Adaptations. Still worth a look. 
Too Cool For Grownups
 http://www.tcfg.com/
A bit of a mix of different activities but the Science Junction is worth a look at.
Another bit of a mix of different activities but again it is worth a look at.
Extreme Science
 http://www.extremescience.com/
As the name suggests, this site looks at extremes in the biggest, baddest and the best are in the natural world. It also presents world records in science and some of the scientists who are working on them
Featured again, Frank Potter at the head of this page says "The complex and abstract nature of Science makes the subject difficult to understand", but "the subject is made much more difficult by the presence of "Science Myths" ...which have become so common and widespread that they even appear in science textbooks and are taught as facts in elementary school." Check out whether you're right or not here.
If you haven't involved yourself in a Family Science Program then you haven't yet been involved in some serious science fun. Not sure how to go about it then go to this Victorian Department site and admire the handiwork of Rob Nelson. The site contains just about anything you might need to run Family Science except the families, (you supply them). Great stuff.

Double Helix Experiments
 http://www.csiro.au/helix/experiments/index.html

If you want some excellent experiments to try at home, these pages from the very popular CSIRO Double Helix Club are a lot of fun even if you aren't a member. If you do like them then why not join the Double Helix Club.
If lesson plans are you go then have a look at this ever expanding list of ideas. Interesting to see how our US cousins approach teaching.
Another Public Broadcasting Service allied site, (doesn't it make you wish that the ABC or SBS could do something like this), it invites contributions from children. It has a most impressive archive of activities and an excellent look at how to design a good science investigation. Check it out.