There is a link within BBC Teachers called Bitesize with videos, activities and lessons.
It is a section for teachers on various topics from ages 5 - 11 that have very short video clips.
http://www.bbc.co.uk/schools/scienceclips/index_flash.shtml
This Bitesize link shows topics on Science, Math and English.
http://www.bbc.co.uk/bitesize/ks2/