Now, this trick doesn't work for all videos, but if you type:


at the end of the address and refresh the page, it'll play the video in high def format and provide a small link below the video to return to normal video playback mode. Here's a horrible example:

Normal Quality:


High Quality:

The second video will take a little longer to load, but you'll easily notice the difference in sound and video quality. Try it out when you find music or videos that don't offer the high quality playback mode. It may not always work for the video, but it's usually worth a shot for the audio.

Better example:

Normal Quality:

High Quality:
If you have Firefox, using this is much more convenient (not to mention it has numerous other features). =)
I suggest creating an account and setting the video playback options. If you choose the fast connection option then you will always see high quality videos when they are available. (On the YouTube site at least. I'm not sure about YouTube videos embedded on other sites.)