YouTube Download

YouTube in Education - many tips and links (note the tool from the Google blog site has been made ineffective and it's best to use one of the Firefox add-ons.)

YouTube Download Tools - Add-ons for Firefox (must be downloaded and installed from within Firefox.)  This link includes:
Video Download Helper 
1-Click YouTube Video Download
Download YouTube Videos + 

You may still end up with a file in .flv format (a Flash format) wihich won't play well in most standard media players.  You may want to convert the .flv file to a standard format using a tool such as Format Factory – an easy to use (free) file converter (Windows only.)  There are also web based converter sites.