Gooru is a service that aims to provide teachers and students with an extensive collection of videos, interactive displays, documents, diagrams, and quizzes for learning about topics in math, social studies, and science. As a Gooru member you have access to hundreds of resources according to subject areas such as social studies, chemistry, biology, ecology, algebra, calculus, and more. Within each subject area you can look for resources according to media type such as video, interactive display, slides, text, and lesson plans. When you find resources that you want to use, drag them to the resources folder within your account. Gooru also offers you the option to add resources to your folders even if you did not find them within Gooru.
MIT Tech TV is a collection of thousands of videos produced by students and faculty at MIT covering topics in engineering, education, science, the humanities, and more. Roughly 300 of the MIT Tech TV videos are also available on their YouTube channel There are a couple of playlists within the channel that could be of interest to high school and middle school science teachers. MIT Engineering K-12 is a set of twenty-six videos in which MIT students explain and demonstrate things like gas pressure, gravity, Boyle's Law, and the shape of sound waves. MIT Physics Demonstrations is a playlist of 44 short demonstrations. The videos don't have narration, just the demonstration. The explanation of the principle demonstrated is found in the description below each video.
The Spangler Effect is a YouTube channel from Steve Spanglere Science. Unlike his popular Sick Science videos which are no more than short demonstrations of science experiments students and parents can do at home, The Spangler Effect videos offer longer (15 minutes or so) explanations of science experiments. The Spangler Effect videos explain the science of do-it-yourself experiments and how you can recreate those experiments at home or in your classroom.