Zemanta expands the author's regular blogging dashboard, populating it on the fly with content suggestions relevant to the current text. It presents images, links, articles, tags in a simple interface. It encourages re-use and linking to other content with as little effort as possible - a single click.
Main features of Zemanta are: On the fly contextual suggestions of related articles, images, links and tags, affiliate linking support, spam-free database of 50.000 news sources and blogs, copyright filtering of suggested images
Sources: Links: Wikipedia, IMDB, Rotten Tomatoes, Amazon, CrunchBase, Google Maps, Last.fm, YouTube, MusicBrainz, Snooth wines, Wikinvest, Muzu.tv, ChaCha, Uptake. Images: Getty, Flickr, Wikipedia. Articles: Major news sources like BBC and CNN and over 50,000 blogs.
You can also try it out without installing the plugin through browser extensions.