These few websites will provide you great tools to download youtube videos or convert them into Mp3, Avi, 3GP or Mp4 for iPhone, iPod .
1.KeepVid - Easy to use and they also have toolbar for easy youtube video download.
2. WikiHow - Few methods that will give you enough info on how to download videos to iPod
3. Vixy - Best tool out there! Allows you to convert flv files online into mp3 or any other file you can think of!!