I've frequently wanted to download videos from Youtube so I would not have to visit the site and wait for the download everytime I wanted to view the video.  There are many free tools to download the videos, but most download it in the native .flv format, which requires a standalone Flash Video player to play. 

With the Free FLV Converter, you can download the video and by default, it will convert the file to AVI format for play with Winamp or Microsoft Video Player.  Be sure to set the output path so you can find the file after download, and then paste the URL into "Add link" box and press "Add".

When you install Free FLV Converter, be sure to disable the Dealio toolbar (it is adware) and the option to Set Yahoo! as my default search engine to keep from cluttering up your browser with unnecessary toolbars and changing your search preferences.