Science is something that is often difficult to organise in the classroom due to time, mess and often resources. These web sites have some great little practical exercises, experiments and explanations of scientific events in simple language students and teachers.
e-learning for kids - is full of animated, and interactive science based tasks.
Active Science - Is full of science themed activities targeted at middle years students including teacher notes.
Popular Science - contains some quirky science to spark interest in science in your classroom.
PBS Kids Science - Some simple science experiments to explore how and why things occur in the world of Science.
let me know if you have any more that need to be included.