The Museum of Science & Industry in Chicago has an online science page for science educators.
The online science page has: videos, activities, and podcasts. The activities include online games/simulations on Simple Machines, Garden in a Glove, and a Worm Farm. There are currently only 3 videos- but see the Baby Chick Hatchery below. The Podcast library has 7 different sessions.
Applications for Science Teachers: Another resource for some interactive science resources. The total number is limited but I think this is a site to watch. Seems most appropriate for Elementary science instruction.
Vodpod videos no longer available.
Science for All 