Opens a new window with rel="external" instead of having to use target="_blank" or target="_new"
rel="external" is now the XHTML valid version that informs search engine spiders that the link is external. However, using this does not open the link in a new window. target="_blank" and target="_new" does this, but is not XHTML valid.
This very simple plugin adds a small JS file to your header to let this happen!