Check out WatchKnow! This is an awesome website that has thousands of educational videos that have been categorized by subject, by age and much more. WatchKnow is an awesome resource for teachers, students and even parents!
There is so much offered on this site that the only way to get a good idea of what there is, is to check it out yourself here! They are always adding more!
(The side picture shows just a sample of the categories and areas of video offered.)