Check out this page full of amazing videos of quick, simple, cheap science demonstrations – on the site of Arvind Gupta. They’ll make you want to have a go. You should also check out this page filled with ‘science toys’.
According to his profile on TED.com, Arvind Gupta is “an Indian toy inventor and populariser of science for kids.” You can see him demonstrate some of his science toys and hear him speak in his TED talk. Entertaining.