What theme are you using? Where did you download it from?
Looks like Suffusion Theme
I’m seeing a code fragment in your sidebar, an iframe that was not closed. It looks like this:
<iframe allowtransparency="true" scrolling="no" frameborder="no" </div>
The iframe is missing a right bracket, and doesn’t seem to have a closing tag. I’m going to take a guess and say look at the widget code for the YouTube link right before it to see if maybe this fragment crept in there.