Credit:
KickYouTube serves up an elegantly simple solution: simply go to the YouTube video you'd like to download and insert the word "kick" at the start of the URL. The final url would look something like http://kickyoutube.com/watch?v=39pZ1r3MG2Q, and options to download the clip are provided at the top of the page.
You don't need me to tell you that having YouTube in your URL is blatant trademark infringement, however, so don't expect this method to work for long. For more solutions, try our list of 20 ways to download YouTube videos...most of which have avoided the wrath of Google's lawyers.
[via Lifehacker]