The Howard Hughes Medical Institute is known for offering to educators free DVDs and other resources about various biology and health topics, such as human evolution, disease, biodiversity and medicines, stem cells, and cloning. They are now offering three new DVDs: The Origin of Species, The Double Helix, and The Day the Mesozoic Died. The Origin of Species consists of three separate videos telling the story of Darwin, Wallace, and evolution and action. The Double Helix covers the history of the discovery of the structure of DNA, and thankfully does not leave out Rosalind Franklin. My son has already watched the one on dinosaur extinction, and at 7 years old, was fully engrossed in the narrative.
If you are a teacher or educator in some other capacity, or perhaps run a discussion group, these are great resources to have. The ordering page is here (select “DVD” on the left to narrow down the selections).