GoldCock (probably). Firefox extension which allows you to download video directly from Youtube. Da da da da da, I'm lovin it.
And here is a bonus link, which teaches you how to search for only the High Quality Vids on youtube: (also ace)
www.labnol.org/internet/video/search-high-resolution-youtube-videos/5228/
(, Mon 19 Jan 2009, 0:30, Reply)
You can always add &FMT=18 to the end of a YouTube url for the high quality version. Not all have it.
If you have an app that searches all HD YouTube posts that would be mega handy!
EDIT
&FMT=22 is for HD videos.
(, Mon 19 Jan 2009, 0:46, Reply)