This is a group at MIT that produce educational and entertaining Science videos. They also have a youtube channel with more videos posted. These instructional videos can be used in all grades, though they do seem to focus more on the high school level. These would be great to use to introduce new concepts or to complement a larger lesson. Some limitations with this would be the choice of content and the depth of content. They look like they haven't been making videos for very long, so the selection is limited. They also go fairly in depth into the subject matter, so it may be beyond the scope of a lesson that you are intending.

They have a huge resource of case studies that can be used in science classrooms of all ages

Great source for science simulations. I use these as inquiry introductory activities where students must use the simulation to discover basic principles of new ideas.

This is software that is used for simulations, and can even be programmed for multiple computers to connect to each other and interact within the simulation.