This youtube user allegrosjf has brief (less than one minute, to a few minutes max) video clips on SCIENCE subjects such as tarantulas, birds, solar system and planets, arthropods etc.
Recommended for grades 2-5 but perfect snippets for younger kids attention spans. From the acclaimed Science Screen Report DVD series from the 70s.
http://www.youtube.com/watch?v=dS8frODupEc&feature=related
http://www.youtube.com/watch?v=JcwT3yxCUsM&feature=mfu_in_order&list=UL
Here’s a LONG one…
http://www.youtube.com/watch?v=rb8HYbWyCpU&feature=mfu_in_order&list=UL