For those of you new to the concept, you`ll need to know a couple of things. Many of these sites and tools simply grab YouTube (YouTube) videos in their native Flash format (FLV). To watch these files on your desktop, you`ll either need to get yourself an FLV player or convert the files into another format you can watch in your media player of choice (or on your iPod/iPhone, cell phone, or wherever the videos will ultimately end up).
Some of the listed tools include Youtube downloads or file format converters for windows. Choose your poison according to your needs and patience level - if you do a lot of downloading it might be worth your while to check out the more full-featured apps.
And now, on with the list!
Windows Applications
1. My Video Downloader With all these free tools, it`s actually funny to see a commercial one. It`s called My Video Downloader, and while it does look solid and offers a lot of conversion options (a free trial which enables you to download 10 videos is available), we`re not sure it offers enough to warrant a price tag.
myvideodownloader.com
2. VDownloader
It is a desktop application that catches YouTube, Google Video, and Grinvi video links from your clipboard. Start it up, copy the video URL and click download. It automatically converts the videos to mpeg or avi formats.
www.softpedia.com/progDownload/VDownloader-Download-51327.html
3. YouTube Grabber
YouTube Grabber downloads files from Youtube in .flv format. Copy and paste the URL of a video from YouTube into the program, press «grab», and the file will be downloaded into the same directory as the program.
www.download.com/Youtube-Grabber/3000-2071_4-10574801.html
4. TubeSucker
TubeSucker is a desktop YouTube video downloader with some interesting options, including batch downloading large amounts of videos from a certain user. See the video tour on the site.
www.newrad.com/software/tubesucker/
5. VideoGet
It boasts being able to download video clips from more than 100 video sharing websites. We haven`t tested all of them, so we`re just going to take their word for it. It`s a deskop application with a nice, simple interface, and a solid number of options.
nuclear-coffee.com/php/products.php

6. Orbit Downloader
It is a desktop application which can download videos from a wide variety of sites. The download process is very simple, just hover your mouse over the video and you`ll get a button that says «Get It». The developers of the program claim that it’s very fast (up to 500% faster, they say) due to its P2P download technology.
www.orbitdownloader.com
7. KeepV
It is a desktop downloader as well as a converter, which can convert the downloaded videos from flv to avi, mov, mp4, or 3gp formats.
keepv.com
8. Wondershre youtube downloader
It comes with a bunch of features, including a built-in FLV player so you can watch videos without needing a separate Flash player or waiting for a file conversion. If you want the file conversion, this app covers that too, and can save the video to MPEG, WMV, iPod/iPhone or 3GP cell phone-typical file formats. It can also extract the audio track and save it as an MP3 or WAV file.
http://www.flash-on-tv.com/youtube-downloader.html
Put YouTube videos on your iPhone, iPod, or any MP4 players is no longer a problem if you have the best video converter. Here is a step by step guide about "Convert YouTube video to MP4" for you, it's easy to understand and works pretty well for me