YouTube for Education is now open for schools to sign up. This service gives access to thousands of educational videos and can be customized to meet the needs of the school. Without having to go around a filter, you can go directly to YouTube.com/education where comments are disabled and content is appropriate for school. To get started, send this link to your network administrators.
Some great examples found on YouTube for Education:
Khan Academy (math): http://www.youtube.com/user/khanacademy
The Periodic Table of Videos (science): http://www.youtube.com/user/periodicvideos
The Portrait Art (drawing/art): http://www.youtube.com/user/ThePortraitArt
CCProse (English/literature): http://www.youtube.com/user/CCProse