Mainly i use keepvids dot com for downloading the video from youtube. It is continent way of downloading the video.....
I use a program called internet Download manager (Its a program for speeding up your downloads from Rapidshare etc, its a great program) and it has an auto-download feature in the firefox browser so I use that ONLY if I just want a video. If I want for example just an MP3 file I use a program called Youtubedownloader, its free and the best so far.