I use aTube Catcher to download the videos I'm going to use in my lessons. (Free and very easy to use).
"If you want to download and convert videos from YouTube or other popular video sites without having to spend ages doing so, look no further than this no-nonsense software. aTube Catcher allows you to do everything (i.e. the downloading and conversion) from within the same window. All you need to do is paste the link to the video and select the format you want to convert to and aTube Catcher does the business for you - at a very quick pace to boot.
Rather handily, the program can also be used as a standalone file converter, letting you take a FLV file and transform it into a different format using a similar process. The program also dishes up a bevy of useful options, such as the ability to define the quality and resolution of the video, audio channels, codecs and more. All in all, aTube Catcher is a brilliant tool for quickly grabbing cool movies from the most popular video sites."
http://kickyoutube.com/ The video shows how to download YouTube videos.
Zambar: Free online file conversation.