This is a stretch for me because I’m really more of a humanities and social sciences librarian than a science one.
There are several resources I’ve found when starting on this topic. I lived in Philadelphia for four years, so my first stop was the Franklin Institute Resources for Science Learning website. While I found a lot of good information, I didn’t see particularly great videos. My next try was the National Science Foundation classroom resources. The link on the left-hand side will take you to a page with film, TV, and museum exhibits. This looks like a great resource for general multimedia resources. One of the links led me to the Denver Museum of Nature & Science’s video on black holes.
A while back, I started noticing that organization began actively utilizing YouTube and providing lots of great free videos. PBS’s NOVA program and the Smithsonian Institution Museum of Natural History both have YouTube channels.
Last, I checked out the websites of two major science journals, Nature and Science. Nature‘s Audio and Video section links to their podcast series. Science Multimedia Portal provides access to podcasts and video streaming.