I am very fortunate to work in a school district that allows teachers to access YouTube videos. For now my district is the exception to the rule, but hopefully in the future more schools will allow access to YouTube at least at the high school level. The quantity of good, educational content on YouTube is far greater than the quantity available on any other site. If you work in a district that blocks YouTube, there are still ways that you can use YouTube content in your classroom. Here are some tools you can use to download YouTube videos for use on your local hard drive.
Catch YouTube is a free tool for converting and downloading YouTube videos. Catch YouTube offers eight formats for video conversion. The video conversions are fairly quick depending on the length of the video.
YouTube Snips is another good tool for downloading YouTube videos for use offline. To use YouTube Snips simply enter the the url of your chosen video and download the video in your preferred format. YouTube Snips gives you the choice of three formats, MP4, 3GP, and FLV. In my test of YouTube Snips the download was very quick.
Miro is an open source media player available for Mac and Windows. Miro is kind of like iTunes for user generated video websites. After you install Miro you can download videos from YouTube and other video sharing sites directly from Miro. If there is a particular video producer that you like you can subscribe to the video channel. Each video is saved in your media player until you decide to delete it.