Zemanta is a content suggestion engine for bloggers and content creators. It’s marketed as a blogging assistant.
It helps content creators by suggesting links for keywords in the text, tags to use, images and related blog posts. that can be used in blog posts in WordPress, Tumblr, Blogger, TypePad, Moveable Type and more. Originally released for use by bloggers, Zemanta is available in many blogging platforms including WordPress, Blogger, TypePad, Ning, MySpace, LiveJournal, MovableType, and Tumblr, as extensions for Chrome, Firefox and Internet Explorer, as well as some web-based email systems.
I use it not only for additional content, but also to find blogs and do research on a topic. To turn it on (or off) in WordPress, go to Personal Settings in the Users menu. Check or uncheck the box at Additional Post Content just above the Account Details section. You have to turn it off if you want to switch to a browser extension. There are extensions for Chrome, FireFox and Internet Explorer. I just added the Chrome extension because it includes the option of listing your own sources.