I am fortunate that my district subscribes to Discovery Education, which contains excellent videos and other material. It is, however, quite expensive. As an alternative, I have had some luck with PBS Learning Media, which has lots of programs that air on PBS as well as other material useful in the classroom. It is free, and only requires a quick registration after the third use.
NextVista was created by Rushton Hurley (a fantastic presenter, by the way) and hosts free videos, most of which were created by students and/or teachers. The Lightbulb section contains academic videos, but the site also contains Global Views and Seeing Service, which specialize in videos from around the world and service videos, respectively.
And what about YouTube? Of course, there are MANY videos available on YouTube; the concerns come with filtering, inappropriate comments viewable by students, or similar videos displayed along the side. Fortunately, there is a site that can remove the extras, leaving you with only the video you want: ViewPure. You can use ViewPure from their site, or "click and drag" a toolbar icon to use their service from other sites. It's a great way to make use of YouTube videos while censoring it for students.
My last tip... always preview! Never rely on content you think should be safe. Preview it first. Better safe than embarrassed later!
Here's to a fantastic start to the school year!