I'm creating this task to collect useful plugin links. Add them to the task itself or in the comments. :)

Zemanta is a plugin that suggests related articles, links to external resources (such as Wikipedia or Google Maps) and images all while you're writing your blog post. It scans the text and gives you one click access to making your content more dynamic. It also suggests metatags for better SEO. I highly recommend it. This link is to the Wordpress extension library, but you can get Zemanta as a browser plugin, for Joomla or Drupal, etc. 

Open Attribute helps you add licensing information to your site, find creative commons licensed images and give credit where credit is due.