Youtube is a great go-to for videos covering pretty much anything, but it isn't the only collection out there that might be of interest for the classroom. Below are a few more video options for when Youtube yields nothing useful. These are great resources for flipping the classroom, self-access or simply explaining a concept as part of a lesson.
There are many more sites that offer at least some video content among their resources, but these are the top 3 I've found for consistently yielding useful results. Hope you find them useful too!
"We believe that everyone should have the same opportunity to learn. The best way to make this possible, we believe, is to organize into one, super directory the hundreds of thousands of good videos currently available on the Internet. To make this a reality, we invite teachers, instructors and educators to suggest videos for inclusion into our directory, and then to review, approve, and assign those videos into appropriate categories using a wiki framework and philosophy. The videos are the highest quality found on the World Wide Web, cover all major educational topics from elementary to secondary schools (or age range 1 – 18), and are Kid Safe!"
"Classroom Clips allows users to search and explore a wide range of educational content which has been correlated to the Virginia Standards of Learning. Featuring many locally produced programs, users are able to stream video and audio clips on topics such as history, government, science, and art."
The Science and Education section of ehow.co.uk - also available at ehow.com - has videos (and articles) covering a range of topics from how to write a literary essay to how to make a model volcano.