Zemanta is a content suggestion engine for bloggers, it can suggest interesting content to you while writing a post. Zemanta now released a plugin for Windows Live Writer users for getting content suggestions right in WLW.
After installing the plugin, it will show up in right sidebar of the WLW, select the plugin and it will open as a sidebar. It will sugeest content while you write the post. Suggestions will appear when you write atleast 300 characters of a post or click on the button to get content suggestions.
Download the Plugin from here.