YouTube is an amazing resource, with videos on just about any topic. There are animations, videos of demonstrations that you might not be able to do in your classroom, and records of talks by famous scientists. The SciLinks webwatchers have been including them as teacher resources in SciLinks for several reasons: Some of the comments about the videos may contain inappropriate language and some of the “related ” videos suggested on the page may be irrelevant (as well as inappropriate) for the classroom. A recent Free Technology for Teachers blog describes the View Pure tool that strips away the extra “stuff” on the YouTube site, if teachers want to share YouTube videos without all of the extras.
I just discovered another source for videos. The BrightStorm site has “thousands” [their words] of video segments on topics in math and science. The science videos I looked at are not glitzy or loaded with eyepopping graphics and soundtracks with popular music. They basically consist of a teacher at a board, sometimes with an animation. There are three tabs underneath—a summary of the key points, a transcript of the audio portion, and a space for students to log in and post a question. These videos could be useful for students who miss a class, who would benefit from hearing (and seeing) an alternative explanation, or as an overview of the topic students could access outside of class.  Best of all – no ads, unrelated links, or off-color comments!  There are also resources (free) for test prep (SAT, AP, etc.) The collection is worth a look.
 
Graphic: http://www.flickr.com/photos/lwr/3556397980/