The Curiosity Files: Quicksand. My kids loved this study and learned SO MUCH about Quicksand!! I love The Curiosity Files and highly recommend them for a complete study of fun science oddities.
While I was doing that unit study, however, I was also turned on to another great internet resource for homeschool science: Steve Spangler Science. You can find a simple recipe for your own quicksand here. While Steve Spangler sells all kinds of fun science stuff (and if you're like me, it will be hard not to go crazy like a kid in a candy store!) he also has FREE science experiments that you can do with household products. Just the thing to chase away the summer doldrums when it's too hot to play outside and you almost (but not quite) wish it was time for school to start again!!
You can also see him on YouTube here. This guy is cool!