If a picture is worth a thousand words then a video must be good for at least a million. That's why I'm devoting this posting to sharing a variety of sources of video that you may find useful in your own classrooms. I have to admit, I'm a bit partial to video as an instructional and inspirational medium and that bias may cloud my writing so beware.
It may be hard to believe but there is a lot of worthwhile content on YouTube that you could use with your students. Unfortunately, there is also a lot of junk and chances are pretty good that YouTube is blocked by most schools. One solution to this is to use Zamzar to convert the videos to actual video files and download those files to your computer so that you can share them with your students. This negates the need to go through the Internet (and associated filters) in order to share the videos.
When it comes to video quality it's hard to beat the content on United Streaming. Not only do they have great video segments, but they also have lesson plan ideas and many other resources for teachers. The videos are broken down into smaller segments so they are more manageable file sizes and this allows you to show just certain parts of a longer video rather than having to show the entire thing. A subscription is required but many states and districts have purchased licenses so check around to see if your school has access to this great resource.
Another option for video is TeacherTube, which is intended for more educational content and does more policing of content to ensure that videos are appropriate for a k-12 audience. TeacherTube is very similar to YouTube in that you can upload your own content, embed videos and search based on different keywords. Users are encouraged to flag inappropriate content in order to help keep things "clean". Chances are pretty good that this site will be blocked as well but it will be an easier sell to get this unblocked over something like YouTube.
SchoolTube is specifically designed for use in k-12 education. It provides media sharing capabilities and requires that all student created video be moderated by registered teachers and adhere to accepted school guidelines. This site is full of student created videos and provides a safe way for your students to share their masterpieces. They even have a variety of video related contests that students can enter.
Studio 4 Learning is a great collection of professionally produced videos designed to help students learn about different subject areas as well as get help with homework, college prep and even career planning. As teachers, you can even become part of the Tutor Corp and share your knowledge on different subjects to help others. It doesn't appear that you can upload your own video to this particular site.
AFI ScreenNation is still fairly new but it is designed to help students share their videos online. They have a variety of contests that students can enter with their different videos. It isn't clear if they are moderating content of the videos or not and the library of current videos is a bit limited at this point.
If you have some other resources you would like to share I would love to hear about them.