iLounge and the Discussion Forums are read by people in countries all over the world. The legality of DVD-to-iPod ripping will vary based on your country of residence. iLounge does not in any way endorse violation of the valid rights of copyright holders, and strongly recommends that you consult your country's copyright and fair use laws before copying any video content.
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.
Also, you can download HD (720p) YouTube videos directly using Apple's Safari browser (under both Mac OS X and Windows only) and the videos won't need any conversion if you have an iPhone 4. YouTube HD videos are hosted as mpeg-4 AVC files so downloading the source mpeg-4 file means it natively works with the iPhone 4. Only 480p and below videos are still hosted as Flash video files (flv) and they need to be converted.
Of course, you cannot directly download a YouTube video with your iPhone. You must use a computer to do this. There is also an HTML5 version of YouTube that natively works with Safari on the iPhone but you still can't download videos with the iPhone.
Just google search Step by Step Guide on How to Convert as well as Download YouTube to iPhone 5/4S/4/3GS on Mac or Windows.
You will find a step by step guide on how to download and convert YouTube to iPhone 5 compatible format so as to successfully play YouTube on iPhone 5. It also applies to download, convert and play YouTube on iPhone 4S, iPhone 4, iPhone 3GS, iPhone 3G, iPod Touch, iPad, Apple TV, iTunes, QuickTime and etc
I've used it as well but wondering it there are any other good converters which shows Youtube content. Most of them works after paste url address. I waste my time jumping between converter and YT site. Can you recommend any other?