If you're blocked, as many people are with YouTube, you have a few other options.
SchoolTube is one such option. Start here to give yourself a bit of a tutorial as to how best to go about using SchoolTube. Or, start by checking out the Channels or Categories.
TeacherTube is another classroom video option. The Teacher's Resource page is a great resource indeed.
QuietTube is like living in the land of simplicity. Even the webpage is peaceful, most likely by design. Here's a brief snapshot of how that works.
And for the eco-minded, there's Ecotube. Just as you can infer, here's their message: "Ecotube is a community of users and their videos about issues facing the world today from an ecological perspective."
Here you have a portal of all types of videos on a multitude of green themes, classified as such (as detailed exactly from their website):
May the movies run educational and wild in your classroom!!
Letter Y pic: http://etc.usf.edu/clipart/52200/52282/52282_letter_y.htm. Website logos from above mentioned websites.