Unplug Your Kids has a tutorial for making a salad spinner zoetrope. (I didn't even know what a zoetrope was at first, but it sure looks clever and fun!)
I like the simplicity of the preschool activity As We Walk describes here.
I never would have thought of turning a child's umbrella into a jellyfish like Make and Takes did here- but isn't it cute?
The bubble blower tutorial given by How Does She? is something I really, really want to try (I'll let you know how it turns out probably in the next few weeks).
**One reader wrote to say that this is a fun activity, but to warn the kids not to suck in- soap bubbles can burn the throat!**
I've wondered before whether or not making an aquascope would be a worthwhile thing to try. MayaMade has a tutorial here as well as some stories about why they made it and their fun experiences with it.Read here about Frugal Family Fun's great idea for helping a child spend hours of imaginative and independent fun.
Finally, take a look at this odd and wonderful website to find ideas for science experiments you can do with candy.