Downloading videos from youtube is not a big deal if you have a registered account and you are paying some amount but if you like some video, don’t have an account still you like to download it and view some other time from your local computer without wasting more internet bandwidth and time to search video then use the under given tools; Few tools can also convert the video in various other extensions.
Keepvid is a single step tool, you just need to drag and drop the URL from your address bar into the given address bar of keepvid and press the download button to save the video at your desired location on your local system. check the under given URL;
Download youtube videos is a single step online tool like keepvid tool but have a special thing that you can also download videos from other websites also. Check the under given URL for a complete list;
Vixy is simple video download online tool but also have a very good feature. It can also convert the video in many format to view on IPOD, PC or PSP. see the under given URL for a complete list of available features.