The TED site is a great source of talks by inspiring people. The Education section has talks accompanied by animations.
Selected TED talks from the National STEM centre website, they have found talks which are age appropriate and have links to the science curriculum.
Selection of free films from this subscription site.
Suitable for GCSE – includes carbon cycle, ecosystems, diffusion, photosynthesis.
Lots of clips for various biology topics, found by a teacher.