Siemen's Science Day is another great, free resource from Discovery Education. It contains videos, tools, resources, and hands-on activities for 4th - 6th grade students in Earth, Life, and Physical Sciences. The activities are engaging and include instructions, material lists, and even extensions for students to do at home.
New activities are constantly being added and activities are rated based on difficulty. I've even taken some and modified them for older students.
This is definitely a must-see resource for science teachers.
