WatchKnowLearn is a site where you will find videos to use in the classroom. This site is has videos and presentations which are in the different categories making it easier for teachers and students to find what they are looking for.
The videos and presentations are embedded from other sites or have links to other sites. Of course there are other sites such as TeacherTube which are great but the real advantage here is that it is one huge directory.
In order to so this they invite educators to suggest videos for inclusion into the directory, and to review, approve, and assign those videos into appropriate categories using a wiki framework and philosophy. These videos are the highest quality found on the World Wide Web and cover all main curriculum or educational topics from primary to secondary schools.