I remember i wrote a post on How to Watch Youtube videos in High Quality but now there is a trick which enable you to watch the video in 720p widescreen video clips. Its a really simple trick that works with those videos which are uploaded in good quality. Usually by using &fmt=6 or &fmt=18 at the end of the url let you view High Quality video resoulution but instead of that now add &fmt=22 to watch the video in 720 screen resolution.

An example of video is this http://www.youtube.com/watch?v=zlfKdbWwruY. Now watch the same video in 720 by adding &fmt=22 at the end of the url http://www.youtube.com/watch?v=zlfKdbWwruY&fmt=22 and see the difference.