I simply use the Youtube app. However if you want a copy you can get an extension for most web browsers which will add a download button somewhere on a Youtube page. You may need to run the video through a converter to make it iPod compatible.
Firefox and Chrome will probably be your best bet, search their Extensions for "Youtube download". In Chrome I found "VideoDownloader for YouTube". I presently use a similar extension, Youtube to mp3, which adds a button under the video to extract the audio and convert it to mp3. It works quite well for my use.