Tooble lets you browse, search and download any video from YouTube and put it on your iPod, iPhone or Apple TV. You can also save them to watch on your computer.
Tooble automatically converts YouTube video to MP4 format and then sends them to iTunes so that the next time you plug in your iPod or iPhone they'll be there for you to watch.
It's super simple to use, because unlike other similar utilities, tooble is also a stand alone YouTube browser. Right now it's only available for Macintosh, but a Windows version is coming soon.