How to open external links in new window?
The External Links module does exactly that:


  External Links is a small module used to differentiate between internal and external links. Using jQuery, it will find all external links on a page and add an external icon indicating it will take you offsite or a mail icon for mailto: links.
  
  Configuration options:
  
  
  Apply icons to either mailto: or external links or both.
  Configure external links to open in a new window.
  A confirmation message when leaving the site.
  Regular expression inclusion and exclusion of links considered external.
  CSS selector inclusion and exclusion of elements for processing